My favorite new quick fix: MS Office Diagnostics
Rebooting cures a multitude of ills.
Over the past two years I've come to realize that the SharePoint server equivalent is to run the SharePoint Products and Technologies Configuration Wizard (what a mouthful that is). However, my latest discovery is that there is a client equivalent as well.
1. Open Word 2007 (or Excel 2007).
2. Click the Office button.
3. Click the Word Options (or Excel Options) button on the resulting menu.
4. Select the Resources tab on the left.
5. Click the Diagnose button.
6. Start the diagnostic tests and follow the prompts.
The tests will take a few minutes to run, after which the results will be displayed (e.g. 1 defect fixed). At this point you can go back and try the offending procedure again... and most likely, the error will be gone.
Additional info: the relevant executable is located at C:\Program Files\Common Files\microsoft shared\OFFDIAG.EXE. Administrators may find this useful for remote execution at login, etc. for curative or preventative purposes. There's no official way to launch it without user intervention, but you could easily run the file with VBScript or .NET code and then use SendKeys to kick it off.
Feel free to contact me with additional problems that this solves; I'd like to keep an updated list here.