In addition to what Alex and Andre said, let me add that just stoppeing and restarting DP may be needed to clear this error. They are both right, but, that alone may not clear the problem.
If you have never run a purge of filenames, or can't remember the last time it was done, you can count on it taking a long time. Referring to Andre's post, the commmand he is referring to is
omnirpt -report db_purge_preview
which will give you a very rough estimate of the time it will take. Note, that you do not have to purge everything at once, you could also run
omnidbutil -purge -filenames [hostname] -force Do not include the [ ] marks
to purge filenams for one or more servers at a time. If you need to stop a purge, run
omnidbutil -purge_stop
This will stop the purging processes, and write a checkpoint into the IDB, so that, when you are able to start the purge again, it will pick up from this point
Yo would think that after the purge is done, you should run a 'writedb/readdb' to recapture the disk space