"Can't Unblock Contact" Error in MSN Messenger for Mac

MSN Messenger for Mac occasionally experiences a problem where blocked contacts cannot be unblocked using the application. This isn't a problem with MSN servers or the contact you've blocked; it's a temporary problem with the Mac application and can be fixed by deleting a temporary file in your user library.

Restart MSN

The first step to solving a temporary problem like this is seeing if a simple restart will fix it. Sign out of MSN, then close the program completely by pressing "Command" and "Q" simultaneously. Doing a complete restart, as opposed to simply signing out, can sometimes refresh temporary problems.

Clear Account History

If you are still experiencing the same issue, clear your program's account history, which will refresh all of your account data, including your block list. Sign out of MSN; then before signing in again, click "Clear Account History." Attempt to sign in normally, then check whether you can unblock your contacts.

Delete User Library File

If all else fails, deleting your Messenger cache file will help refresh everything. Sign out of MSN, then close it completely like before. Open a new Finder window, then navigate to "/user/library/preferences/microsoft/." Locate the file named "Microsoft Messenger User Cache.plist" and delete it. Start up MSN again and sign in; you should now be able to unblock your contacts without a problem.

Considerations & Alternatives

Since the problem is located only in your program, if you have having difficulty, you can sign onto MSN online, either through MSN.com services or an online chat client like Meebo, then unblock your contacts from there. You can also try reinstalling or simply updating your MSN application to see if any updates fix a bug that could be causing the program.