I had the same problem and found the following solution:
PSPad - "Can not delete output file C:\Program Files\PSPad
editor\PSPadShell.dll"
If get the above error when unzipping a PSPad cab file with 7-Zip:
1. Run the file PSPadShell_unreg.bat (in the PSPad program folder).
2. Start PSPad.
3. Ensure that Windows Explorer (or Total Commander) is not running.
4. In PSPad "Settings/Program Settings/System Integration" uncheck
"Multi User
Environment".
5. Exit PSPad
6. Replace PSPadShell.dll (run 7-Zip on the cab file again)
7. In PSPad "Settings/Program Settings/System Integration" check "Multi
User
Environment".
8. Run the file PSPadShell_reg.bat (in the PSPad program folder).
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PSPad freeware editor http://www.pspad.com
