"Cannot uninstall Language Pack" and Unexpected System.NullReferenceException when trying to access the web site

How to fix this error

The message "Cannot uninstall Language Pack" appears when doing Uninstall-SPSolution and an Unexpected System.NullReferenceException appears when trying to access the web site. This error may only be present on one of the servers in a farm.

1. Stop the SharePoint Timer Service (OWSTIMER).
2. On the problem server, navigate to:
1. Windows Server 2003 location: Drive:\Documents and Settings\All Users\Application Data\Microsoft\SharePoint\Config\GUID and delete all the XML files from the directory.
2. Windows Server 2008 location: Drive:\ProgramData\Microsoft\SharePoint\Config\GUID and delete all the XML files from the directory.
3. Delete all the XML files in the directory or sub directories, not the .INI file.
4. Open the cache.ini with Notepad and reset the number to 1. Save and close the file.
5. Start the service on the server and wait for XML files to begin to reappear.
6. IIS Reset