A couple users have noticed problems with MarsEdit 1.2 after agreeing to update the Keychain for MarsEdit and then attempting to refresh their blogs or post a new post:http://www.red-sweater.com/forums/viewtopic.php?id=250
It's been discovered that at least in one case, deleting the Keychain Access item(s) for MarsEdit (you'll have to enter your passwords again, so reveal them and write them down if necessary) works around the problem.
I'm going to be looking into the root cause of this problem, and if it is indeed something that MarsEdit is doing, fix it ASAP. But as a workaround try deleting the keychain passwords:
1. Open Keychain Access (/Applications/Utiltiies/Keychain Access)
2. Find MarsEdit password items (type MarsEdit into the search filter field).
3. Select MarsEdit items and delete them after writing down the associated password, if necessary.
I apologize for the inconvenience and hope to get to the *real* bottom of this soon.