Method 1: Fixing the DLL Error by Copying the Iisext51.dll Library to the Windows System Directory 

1. The file you are going to download is a compressed file with the ".zip" extension. You cannot directly install the ".zip" file. First, you need to extract the dynamic link library from inside it. So, double-click the file with the ".zip" extension that you downloaded and open the file.
2. You will see the library named "Iisext51.dll" in the window that opens up. This is the library we are going to install. Click the library once with the left mouse button. By doing this you will have chosen the library.

   

3. Click the "Extract To" symbol marked in the picture. To extract the dynamic link library, it will want you to choose the desired location. Choose the "Desktop" location and click "OK" to extract the library to the desktop. In order to do this, you need to use the Winrar program. If you do not have this program, you can find and download it through a quick search on the Internet.

   

4. Copy the "Iisext51.dll" library file you extracted.
5. Paste the dynamic link library you copied into the "C:\Windows\System32" directory.

   

6. If you are using a 64 Bit operating system, copy the "Iisext51.dll" library and paste it into the "C:\Windows\sysWOW64" as well.

   NOTE! On Windows operating systems with 64 Bit architecture, the dynamic link library must be in both the "sysWOW64" directory as well as the "System32" directory. In other words, you must copy the "Iisext51.dll" library into both directories.

   

7. In order to complete this step, you must run the Command Prompt as administrator. In order to do this, all you have to do is follow the steps below.

   NOTE! We ran the Command Prompt using Windows 10. If you are using Windows 8.1, Windows 8, Windows 7, Windows Vista or Windows XP, you can use the same method to run the Command Prompt as administrator.

   1. Open the Start Menu and before clicking anywhere, type "cmd" on your keyboard. This process will enable you to run a search through the Start Menu. We also typed in "cmd" to bring up the Command Prompt.
   2. Right-click the "Command Prompt" search result that comes up and click the Run as administrator" option.

   

8. Paste the command below into the Command Line window that opens and hit the Enter key on your keyboard. This command will delete the Iisext51.dll library's damaged registry (It will not delete the file you pasted into the System32 directory, but will delete the registry in Regedit. The file you pasted in the System32 directory will not be damaged in any way).

   %windir%\System32\regsvr32.exe /u Iisext51.dll

   

9. If you are using a Windows version that has 64 Bit architecture, after running the above command, you need to run the command below. With this command, we will clean the problematic Iisext51.dll registry for 64 Bit (The cleaning process only involves the registries in Regedit. In other words, the dynamic link library you pasted into the SysWoW64 will not be damaged).

   %windir%\SysWoW64\regsvr32.exe /u Iisext51.dll

   

10. You must create a new registry for the dynamic link library that you deleted from the registry editor. In order to do this, copy the command below and paste it into the Command Line and hit Enter.

    %windir%\System32\regsvr32.exe /i Iisext51.dll

    

11. If the Windows version you use has 64 Bit architecture, after running the command above, you must run the command below. With this command, you will create a clean registry for the problematic registry of the Iisext51.dll library that we deleted.

    %windir%\SysWoW64\regsvr32.exe /i Iisext51.dll

    

12. If you did the processes in full, the installation should have finished successfully. If you received an error from the command line, you don't need to be anxious. Even if the Iisext51.dll library was installed successfully, you can still receive error messages like these due to some incompatibilities. In order to test whether your dll issue was fixed or not, try running the program giving the error message again. If the error is continuing, try the 2nd Method to fix this issue.

Method 2: Copying the Iisext51.dll Library to the Program Installation Directory 

1. First, you need to find the installation directory for the program you are receiving the "Iisext51.dll not found", "Iisext51.dll is missing" or other similar dll errors. In order to do this, right-click on the shortcut for the program and click the Properties option from the options that come up.

   

2. Open the program's installation directory by clicking on the Open File Location button in the Properties window that comes up.

   

3. Copy the Iisext51.dll library into the directory we opened.

   

4. The installation is complete. Run the program that is giving you the error. If the error is continuing, you may benefit from trying the 3rd Method as an alternative.

Method 3: Doing a Clean Reinstall of the Program That Is Giving the Iisext51.dll Error 

1. Press the "Windows" + "R" keys at the same time to open the Run tool. Paste the command below into the text field titled "Open" in the Run window that opens and press the Enter key on your keyboard. This command will open the "Programs and Features" tool.

   appwiz.cpl

   

2. On the Programs and Features screen that will come up, you will see the list of programs on your computer. Find the program that gives you the dll error and with your mouse right-click it. The right-click menu will open. Click the "Uninstall" option in this menu to start the uninstall process.

   

3. You will see a "Do you want to uninstall this program?" confirmation window. Confirm the process and wait for the program to be completely uninstalled. The uninstall process can take some time. This time will change according to your computer's performance and the size of the program. After the program is uninstalled, restart your computer.

   

4. After restarting your computer, reinstall the program that was giving the error.
5. This process may help the dll problem you are experiencing. If you are continuing to get the same dll error, the problem is most likely with Windows. In order to fix dll problems relating to Windows, complete the 4th Method and 5th Method.

Method 4: Fixing the Iisext51.dll error with the Windows System File Checker 

1. In order to complete this step, you must run the Command Prompt as administrator. In order to do this, all you have to do is follow the steps below.

   NOTE! We ran the Command Prompt using Windows 10. If you are using Windows 8.1, Windows 8, Windows 7, Windows Vista or Windows XP, you can use the same method to run the Command Prompt as administrator.

   1. Open the Start Menu and before clicking anywhere, type "cmd" on your keyboard. This process will enable you to run a search through the Start Menu. We also typed in "cmd" to bring up the Command Prompt.
   2. Right-click the "Command Prompt" search result that comes up and click the Run as administrator" option.

   

2. Type the command below into the Command Line page that comes up and run it by pressing Enter on your keyboard.

   sfc /scannow

   

3. The process can take some time depending on your computer and the condition of the errors in the system. Before the process is finished, don't close the command line! When the process is finished, try restarting the program that you are experiencing the errors in after closing the command line.

Method 5: Getting Rid of Iisext51.dll Errors by Updating the Windows Operating System 

Some programs require updated dynamic link libraries from the operating system. If your operating system is not updated, this requirement is not met and you will receive dll errors. Because of this, updating your operating system may solve the dll errors you are experiencing.

Most of the time, operating systems are automatically updated. However, in some situations, the automatic updates may not work. For situations like this, you may need to check for updates manually.

For every Windows version, the process of manually checking for updates is different. Because of this, we prepared a special guide for each Windows version. You can get our guides to manually check for updates based on the Windows version you use through the links below.

Guides to Manually Update for All Windows Versions 

1. Guide to Manually Update Windows 10
2. Guide to Manually Update Windows 8.1 and Windows 8
3. Guide to Manually Update Windows 7 and Windows Vista
4. Guide to Manually Update Windows XP