I first described the subject behavior, and a possible resolution, at tip 5140 ยป A file that is required to run the Windows XP Search Companion cannot be found?

Another possible cause of the A file that is required to run Search Companion cannot be found error is corruption in the msxml3 library registration information.

To resolve this issue:

1. Open a CMD.EXE prompt.

2. Type the following commands, pressing Enter after each line:

cd /d "%SystemRoot%\System32"
regsvr32 /u /s msxml3.dll
regsvr32 /s msxml3.dll