Transactional Replication Problem

I have the following error when i start synchronizing the db from
publisher to subscriber manually. Please help me out to find the
solution of this problem.

The replication agent has not logged a progress message in 30 minutes.
This might indicate an unresponsive agent or high system activity.
Verify that records are being replicated to the destination and that
connections to the Subscriber, Publisher, and Distributor are still