STSADM is your friend
If you haven’t used the command line utility available in SharePoint then I’d encourage you to get to grips with it. You can do all sorts of things with it including installing solutions, features, creating sites etc. For a full listing type
stsadm.exe –help
You can find the stsadm.exe in the bin directory on the 12 hive…”C:\Program Files\Common Files\Microsoft Shared\web server extensions\12”
On my SharePoint development server a whole bunch of testing features and solutions had been deployed. Anyway when working on an unrelated project I noticed I could no longer view the site columns on the root site. I just received the helpful error message…
KeyNotFoKeyNotFoundException: The given key was not present in the dictionary Exception: The given key was not present in the dictionary
So what now? well using a console app I iterated through the web fields and could see that an exception was been thrown at a custom field. So using STSADM I looked through the solutions deployed to SharePoint
STSADM –o enumsolutions
I spotted the solution that was causing the problem then retracted the solution (which removed the solutions assets from the 12 Hive and GAC where applicable, then deleted the solution)
STSADM –o retractsolution –name NAMEOFSOLUION.WSP –local
For a listing of all the retractsolution attributes just type
STSADM –help restractsolution
then removed the solution
STSADM –o deletesolution –name NAMEOFSOLUTION.WSP
So I guess a couple of morals to this story, Don’t leave your test code deployed up in your test SharePoint servers and get to grips with STSADM it can really help you in times of need. Plus working from a DOS prompt brings back some happy memories to me, doing Lotus CC:Mail post office reclaims and the like. – Ahh happy days 
