I get this error when I want to edit a block. This makes me unable to edit it, I shut down Norton Virusscanner/Firewall, so that isn't it.

I can make new blocks, just not edit existing ones

help!

Go into your groups admin, and investigate what this block is. Each block is assigned a number as it's created. Once you have that information, go to your cache setting of that block and disable the cache until you have made your changes. Or you can optionaly delete the files in you /cache folder.

I've run into this from time to time when changing /cache settings. You may want to disable module wide cache settings in your general preferences. Check each block your using through block administration for cache settings that you may have inadvertantly enabled.