Can you please give us the error message in details.
What I can suggest is you can probably turn off the logging temporarily, take a full backup. Do some dummy transactions like creating a temp table and inserting a few records. Now take a fresh backup and restore this to a diff alais and turn on logging, see if this works, if it does then do the same for the original db.
This is a wild shot.. lets hope this helps.
Meanwhile please post the error that you get in the db2diag.log or on your console