If you have been having problems with CRM 4.0 Mail merge giving you the following error and you are using Quickbooks Time Tracker, try disabling the Time Tracker add in for Outlook and see if it solves your problem. To test if this is the issue, disable the Time Tracker add in and retest the mail merge. I have installed the latest patch to no avail. Disabling the Time Tracker add-in seems to be the only fix I can find.
If anyone knows how to make them play well together, please drop me a note.