Ah, looks like another problem with MySQL running set in strict mode.
What you can do is run the following SQL command to disable strict mode, and then I'll need to fix that in the base code:
SET GLOBAL SQL_MODE=''
As for deleting. For multiple rss feeds, you can disable them (once you run that query) and then delete the .xml file from the cache directory. I'll need to alter the code to delete the .xml file when a feed is disabled.