From a newsgroup post: "Here are the steps I took to correct these errors:
1. I downloaded a wonderful, free (yes, FREE!) utility called SharePoint Inspector, created by Gat Bouveret (see the link to “SharePoint Inspector” below). I used this tool to identify the web applications and sites referred to by their GUID in the event log errors.
2. I opened a command prompt and typed stsadm- o preparetomove –Site <site> –OldContentDb <GUID of the contentdb listed in event log error>.
3. After this completed successfully, I ran stsadm –o sync –deleteolddatabases 0 (note: Depending on how long you’ve been seeing these errors, you may be able to use a switch greater than zero. If it’s been 2 days since it synched last, you can use 2. You can tell this by typing stsadm –o sync –listolddatabases <number of days you think> and look for the offending content db GUID.
In my case, there were 4 “my site” sites that were not syncing with the profile database. After performing these steps, I rechecked the event log at the top of the hour and the events had not reoccurred". See the link to "Failure trying to sync" for the original post.
You can try to run "stsadm -o sync -DeleteOldDatabases".