Method 1: Installing the Qd3dts91.dll Library to the Windows System Directory 

1. The file you will download is a compressed file with the ".zip" extension. You cannot directly install the ".zip" file. Because of this, first, double-click this file and open the file. You will see the library named "Qd3dts91.dll" in the window that opens. Drag this library to the desktop with the left mouse button. This is the library you need.

   

2. Copy the "Qd3dts91.dll" library and paste it into the "C:\Windows\System32" directory.

   

3. If your operating system has a 64 Bit architecture, copy the "Qd3dts91.dll" library and paste it also into the "C:\Windows\sysWOW64" directory.

   NOTE! On 64 Bit systems, the dynamic link library must be in both the "sysWOW64" directory as well as the "System32" directory. In other words, you must copy the "Qd3dts91.dll" library into both directories.

   

4. 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.

   

5. Paste the command below into the Command Line window that opens up and press Enter key. This command will delete the problematic registry of the Qd3dts91.dll library (Nothing will happen to the library we pasted in the System32 directory, it just deletes the registry from the Windows Registry Editor. The library we pasted in the System32 directory will not be damaged).

   %windir%\System32\regsvr32.exe /u Qd3dts91.dll

   

6. If the Windows you use has 64 Bit architecture, after running the command above, you must run the command below. This command will clean the broken registry of the Qd3dts91.dll library from the 64 Bit architecture (The Cleaning process is only with registries in the Windows Registry Editor. In other words, the dynamic link library that we pasted into the SysWoW64 directory will stay as it is).

   %windir%\SysWoW64\regsvr32.exe /u Qd3dts91.dll

   

7. 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 Qd3dts91.dll

   

8. 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 Qd3dts91.dll library (We deleted the damaged registry with the previous command).

   %windir%\SysWoW64\regsvr32.exe /i Qd3dts91.dll

   

9. You may see certain error messages when running the commands from the command line. These errors will not prevent the installation of the Qd3dts91.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 Qd3dts91.dll Library Into The Program Installation Directory 

1. First, you need to find the installation directory for the program you are receiving the "Qd3dts91.dll not found", "Qd3dts91.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 Qd3dts91.dll library.
4. Paste the dynamic link library you copied into the program's installation directory that we just opened.

   

5. When the dynamic link library is moved to the program installation directory, it means that the process is completed. Check to see if the issue was fixed by running the program giving the error message again. If you are still receiving the error message, you can complete the 3rd Method as an alternative.

Method 3: Uninstalling and Reinstalling the Program That Is Giving the Qd3dts91.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. 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. You can fix the error you are expericing with this method. If the dll error is continuing in spite of the solution methods you are using, the source of the problem is the Windows operating system. In order to fix dll errors in Windows you will need to complete the 4th Method and the 5th Method in the list.

Method 4: Fixing the Qd3dts91.dll Error using the Windows System File Checker (sfc /scannow) 

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. Paste the command in the line below into the Command Line that opens up and press Enter key.

   sfc /scannow

   

3. The scan and repair process can take some time depending on your hardware and amount of system errors. Wait for the process to complete. After the repair process finishes, try running the program that is giving you're the error.

Method 5: Fixing the Qd3dts91.dll Error by Updating Windows 

Most of the time, programs have been programmed to use the most recent dynamic link libraries. If your operating system is not updated, these files cannot be provided and dll errors appear. So, we will try to fix the dll errors by updating the operating system.

Since the methods to update Windows versions are different from each other, we found it appropriate to prepare a separate article for each Windows version. You can get our update article that relates to your operating system version by using the links below.

Guides to Manually Update the Windows Operating System 

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