Our story begins with a standalone server. We had a picker control on a form that we were using to select an employee name from active directory and we kept seeing this error ever so often:
 

Error

The search could not be completed because the server encountered the problem when retrieving results.

If you remember all the way back to the first paragraph where I said this was a standalone server, well that was a lie. As it happens this was a two server farm and one of the servers lost communication with the domain controller. We bounced the pair of servers to resolve this.