Themeui.dll is a process associated with Windows Theme API from Microsoft Corporation. Themeui.dll error messages may appear when you try to install or open a program without its required dll file, or once your PC boots up or shuts down. Such themeui.dll errors are often caused by missing or corrupting the themeui dll file.

Common themeui.dll error messages:
- "Windows could not start because the following file is missing or corrupt: Windows root\system32\Themeui.dll. Please re-install a copy of the above file."
- "Winnt_root>\System32\Themeui.dll missing or corrupt: Please re-install a copy of the above file."
- "Cannot find \Windows\System32\Themeui.dll."
- "Cannot find Themeui.dll."
- "A required .DLL file, Themeui.dll was not found."
- "Program requires the file 'Themeui.dll' to run. Run Setup again to assure proper installation."

How to install themeui.dll file?

1. Press Start and select Run
2. Type CMD and press Enter (or if you use Windows ME, type COMMAND)
3. Type regsvr32 themeui.dll and press Enter
4. In the end, you should receive a message saying that your file was successfully installed or uninstalled.