Before you waste time on trying to fix complex TFS or MOSS problem I suggest doing 5 things.
1. Run an IIS Reset
2. Run 'SharePoint Technologies and Configuration Wizard'
Only #2 on the list because it takes slightly more time than #1. On the other hand, this should fix more problems than any other on the list. This does automatic IIS resets, so you will have temporary downtime.
3. Reboot your machine(s)
4. Make sure account has proper rights
This one is more for stsadm operations and scripts, but most of the time I have found if a command is giving you some strange failurethat it shouldn't, it is more often the account you are using doesn't have the specific right you need for that operation. The command line runat command is your friend for testing this.
5. Install most recent Service Pack/Update
Be sure to check with Microsoft for any updates. SharePoint is one of their most premier products at the moment, and they are spending a lot of time and money developing for it.
Important to note: Recycling your app pools, restarting IIS and rebooting your machine are no-brainers in a dev environment. However in production you need to proceed cautiously. That's why its important to stage a stable prod server with config/settings changes made off-hours with some automated scripts to generate thousands of hits immediately afterwards as this will find 98%+ of potential problems before the users do.