Installation fails with message "Error 2738. Could not access VBScript run time for custom action."

Issue

When you attempted to install or uninstall your product on Windows Vista or Windows 7, the following error appeared and the installation or deinstallation did not continue:

Error 2738. Could not access VBScript run time for custom action.

Solution

This error message indicates that the VBScript engine is not correctly registered on the affected machine.

The VBScript engine can be registered by following these steps:

1. Run Command Prompt as administrator:
1. Start Menu -> All Programs -> Accessories
2. Right click on Command Prompt and select Run as administrator
2. Navigate to the folder that contains the DLL:
• If you are using 32-bit version of Windows:
• Type cd %windir%\system32 into the Command Prompt and press ENTER
• If you are using 64-bit version of Windows:
• Type cd %windir%\syswow64 into the Command Prompt and press ENTER
3. Run the command that registers the DLL:
• Type regsvr32 vbscript.dll into the Command Prompt and press ENTER.

If the problem still persists even after successfully registering the DLL as described above, the most likely cause is that the DLL was already registered by a non administrative user.

In this case you will need to first log onto machine as the user who registered the DLL previously and unregister the DLL as follows:

1. Run Command Prompt:
1. Start Menu -> All Programs -> Accessories
2. Double-Click on Command Prompt 
2. Navigate to the folder that contains the DLL:
• If you are using 32-bit version of Windows:
• Type cd %windir%\system32 into the Command Prompt and press ENTER
• If you are using 64-bit version of Windows:
• Type cd %windir%\syswow64 into the Command Prompt and press ENTER
3. Run the command that unregisters the DLL:
• Type regsvr32 /u vbscript.dll into the Command Prompt and press ENTER.

Next, register the DLL again while running Command Prompt as Administrator, as described above.

For more advanced users, please also check out the following Up and Ready blog post for an additional solution to this issue:

http://upandready.typepad.com/up_and_ready/2011/07/error-2738-installation-could-not-access-vbscript-run-time-for-custom-action.html