1. Add a gadget to yor web.config, for example twitter gadget
2. Add that gadgt on your dashboard
3. Remove the web.config entry
4. Try and add a new gadget, see 500 error
Renaming a gadget also produces this error.
Thanks for posting about bugs. Keep doing this =)
Since the CTP we changed so that these scenarios produce an "error" gadget you can choose to remove from your dashboard (or fix the problem)
1. Add a gadget to yor web.config, for example twitter gadget
2. Add that gadgt on your dashboard
3. Remove the web.config entry
4. Try and add a new gadget, see 500 error