If you remove the Windows 2000 March 2001 Compatibility Update, it may remove the files from SystemRoot%\AppPatch folder, except for Shcmn.dll.
Application of Service Pack 3 may fail to remove the Windows 2000 Application Compatibility Update (March, 2001) entry from Add/Remove programs. The entry should be removed because the update is included in SP3.
NOTE: You may remove the entry using tip 0034.
To workaround this problem, re-apply Service Pack 3.