In ClipMate 7.1, the "parent_id" field of the collection properties dialog is editable, and some users have managed to insert bad data into this field. The ID must be a valid GUID, which is one of those long funny numbers surrounded by {} brackets.
If you get an error at startup complaining about "not a valid GUID", then you can fix the problem with this script.
Code:
update coll set parent_guid = '{00000000-0000-0000-0000-000000000000}' where parent_guid not like '{%}';
Use the startup/recovery screen to get to the SQL dialog, in order to enter this command. Here's how to get there:
http://www.thornsoft.com/phpBB2/viewtopic.php?t=2297