Method 1: Installing the 21755a7.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 "21755a7.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 "21755a7.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 "21755a7.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 "21755a7.dll" library into both directories.

   

7. First, we must run the Windows Command Prompt as an administrator.

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

   1. Open the Start Menu and type in "cmd", but don't press Enter. Doing this, you will have run a search of your computer through the Start Menu. In other words, typing in "cmd" we did a search for the Command Prompt.
   2. When you see the "Command Prompt" option among the search results, push the "CTRL" + "SHIFT" + "ENTER
   " keys on your keyboard.
   3. A verification window will pop up asking, "Do you want to run the Command Prompt as with administrative permission?" Approve this action by saying, "Yes".

   

8. Let's copy the command below and paste it in the Command Line that comes up, then let's press Enter. This command deletes the 21755a7.dll library's problematic registry in the Windows Registry Editor (The library that we copied to the System32 directory does not perform any action with the library, it just deletes the registry in the Windows Registry Editor. The library that we pasted into the System32 directory will not be damaged).

   %windir%\System32\regsvr32.exe /u 21755a7.dll

   

9. If you are using a 64 Bit operating system, after doing the commands above, you also need to run the command below. With this command, we will also delete the 21755a7.dll library's damaged registry for 64 Bit (The deleting process will be only for the registries in Regedit. In other words, the dll file you pasted into the SysWoW64 folder will not be damaged at all).

   %windir%\SysWoW64\regsvr32.exe /u 21755a7.dll

   

10. In order to cleanly recreate the dll library's registry that we deleted, copy the command below and paste it into the Command Line and hit Enter.

    %windir%\System32\regsvr32.exe /i 21755a7.dll

    

11. If you are using a Windows with 64 Bit architecture, after running the previous command, you need to run the command below. By running this command, we will have created a clean registry for the 21755a7.dll library (We deleted the damaged registry with the previous command).

    %windir%\SysWoW64\regsvr32.exe /i 21755a7.dll

    

12. You may see certain error messages when running the commands from the command line. These errors will not prevent the installation of the 21755a7.dll library. In other words, the installation will finish, but it may give some errors because of certain incompatibilities. After restarting your computer, to see if the installation was successful or not, try running the program that was giving the dll error again. If you continue to get the errors when running the program after the installation, you can try the 2nd Method as an alternative.

Method 2: Copying the 21755a7.dll Library to the Program Installation Directory 

1. First, you need to find the installation directory for the program you are receiving the "21755a7.dll not found", "21755a7.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 21755a7.dll library into this directory that opens.

   

4. This is all there is to the process. Now, try to run the program again. If the problem still is not solved, you can try the 3rd Method.

Method 3: Doing a Clean Reinstall of the Program That Is Giving the 21755a7.dll Error 

1. Push the "Windows" + "R" keys at the same time to open the Run window. Type the command below into the Run window that opens up and hit Enter. This process will open the "Programs and Features" window.

   appwiz.cpl

   

2. The Programs and Features window will open up. Find the program that is giving you the dll error in this window that lists all the programs on your computer and "Right-Click > Uninstall" on this program.

   

3. Uninstall the program from your computer by following the steps that come up and restart your computer.

   

4. After restarting your computer, reinstall the program.
5. This method may provide the solution to the dll error you're experiencing. If the dll error is continuing, the problem is most likely deriving from the Windows operating system. In order to fix dll errors deriving from the Windows operating system, complete the 4th Method and the 5th Method.

Method 4: Fixing the 21755a7.dll error with the Windows System File Checker 

1. First, we must run the Windows Command Prompt as an administrator.

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

   1. Open the Start Menu and type in "cmd", but don't press Enter. Doing this, you will have run a search of your computer through the Start Menu. In other words, typing in "cmd" we did a search for the Command Prompt.
   2. When you see the "Command Prompt" option among the search results, push the "CTRL" + "SHIFT" + "ENTER
   " keys on your keyboard.
   3. A verification window will pop up asking, "Do you want to run the Command Prompt as with administrative permission?" Approve this action by saying, "Yes".

   

2. After typing the command below into the Command Line, push Enter.

   sfc /scannow

   

3. Depending on your computer's performance and the amount of errors on your system, this process can take some time. You can see the progress on the Command Line. Wait for this process to end. After the scan and repair processes are finished, try running the program giving you errors again.

Method 5: Fixing the 21755a7.dll Error by Manually Updating Windows 

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.

Windows Update Guides 

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