SQL server 2008 R2 cannot connect to Distributor during WebSync

 I set up a server with SQL 2k8 R2 and want to sync a publication with a remote subscriber.

Everything is basically set up and I am using RMO.  Subscriptions are being created on both server and client (uses Express version) , but when I use 

subscription.SynchronizationAgent

To initialize the subscription on the clients, is gives me an error : 

The process could not connect to Distributor 'MACHINENAME\INSTANCE'.      

at Microsoft.SqlServer.Replication.MergeSynchronizationAgent.Run()
   at Microsoft.SqlServer.Replication.MergeSynchronizationAgent.Synchronize()


What could be the problem ?? How can I check ??