Do you get this error for every search term? What kind of search are you doing?
We are still in our EPDM development stage. This looks like an error we were getting when we tried to do a context search for one the the keywords used in SQL (namely "which"). My IT guy ended up blowing away the whole vault inadvertently while trying to get context searching to work and when he reinstalled, he finally got the context searching to work correctly. We no longer get the error so I can't confirm that it's the same.
Did you recently update EPDM? If so, remove the SWTaskAddin from the addins dialog in the administration tool, and then import it using the Convert.cex file. (Located in the Default data directory.)