RepositoryException during serialization

Hi,

we are using CQ5.4 and in one of our environments I see that both replications queues are active but have over 2k of pending items (for activation and deactivation)

One the replication logs shows a lot of the following error:

ERROR - agent2 : Error while building replication content com.day.cq.replication.ReplicationException: RepositoryException during serialization

The other queue log does not any errors.

Any idea what could have caused this,

Thanks,

Lior