The "Blocked by error" message does write to the server event logs.. can sometimes make out what is going on from there. last few times I have had it it has been.. "Trimservices account is not an acount in trim" and DCI pending file issue.
We just experience the error that you are talking about in the Content Indexing monitor. There was a backlog in the queue that needed to be indexed. This error also was giving us error in Title Word searches and searches within X amount of words.
The windows application log listed the specific error of where it was hung up--In our cast it listed the path to the electronic document and which DCI directory held the index. (In our cast we had our DCI Indexes located on a NAS with all of our Document Stores) In the DCI directory path that was listed in the windows application log error I had to copy the TRIMPending.bin (Just in case) and delete the original. Restart the Workgroup service It started to process the files that were backed up in the queue and the problem was fixed.