sometimes MOSS2007 throws weird errors, to see what is happening it is necessary to open a CMD and execute the following
stsadm -o setlogginglevel -default
There are three things that you also need to check:
1. Check the user permssions for your “SharePoint Tracing Service”.
Go to: Start – Administrative Tools – Services – locate “SharePoint Tracing Service”.
Make sure that user running this service is a member of Local Administrators group.
2. Restart service from step 1.
3. Free up some disk space.