I've encountered this error too, I just close and reopen EPDM search, and it works well.
I think the reason is the Indexing service of the EPDM contained computer's operating system is scanning for content of EPDM's files.
When the Indexing service complete scan content, the problem will not appear again. You can check Indexing service status, go to EPDM server, right-click on My computer, choose manage, Services and Applications, Indexing.
Hope it helps.
I will go on the server and try to restart the indexing service to see if that fixes the problem