After uninstalling an Exchange Client Extension it's possible to get the
message "The add-in *** could not be installed or loaded. This problem may be
resolved by using Detect and Repair on the Help menu" when starting Outlook.

This happens on multi-user systems because the instruction to rebuild the
add-in cache (extend.dat) is a machine-wide registry value and only the first
user to start Outlook gets their cache rebuilt properly.

Does anyone have a solution for this besides deleting extend.dat for every
user?

Note: The machine-wide value I'm referring to is:
HKEY_LOCAL_MACHINE\Software\Microsoft\Exchange\Cli ent\Extensions\
4.0;Outxxx.dll;7;000000000000000;0000000000;OutXXX
Outlook deletes this value after reading it, so subsequent users don't see it.