Unable start or stop merge replication (Push)

Hi,

I have the merge replication (Push)  for SQL Server 2008.The right-click option for Start and Stop Synchronizing in subscriptions has been disabled. How can I stop the merge replication and start again ?

This error happened 1 week after I created the merge replication. The merge data cannot sync to subscriber and only solution I can use is drop and re-create the merge replication again but error would be re-occur a week later.

The merge replication work fine before and start from middle on May 2015, but it keep happen right now.

Any solutions?

Thanks

Teddy