Replication stalling on one subscriber I currently have transactional replication set up for three databases from the same Publisher to the same three Subscribers in SQL Server 2005. Publisher and Distributor are on the same server. 

One of the databases on one Subscriber stops for several hours each day at different times with no indication of why. No problem with all three databases on the other two Subscribers or the other two databases on the problem Subscriber. 

Searching the system logs shows nothing abnormal happening on the Subscriber and Replication Monitor details just says "delivering replicated transactions". Inserting a tracer token shows the Publisher to Distributor is normal.

Any suggestions for troubleshooting this problem?
Finally traced the issue to a table on the Subscriber that was missing the PK index. Still not too sure how this could have happened as all subscribers were initialized from the same snapshot at the same time. Re-initializing the individual subscriber had no affect. 
I had to; 
    - remove the article from the publication
    - run the Snapshot Agent
    - manually drop the table on each Subscriber
    - add the article back to the publication
    - re-run the Snapshot Agent

All good now.