The merge Process Could not enumerate changes at the 'Subscriber'

I am working on a Merge Replication. Server is SQL 2012, Clients are 2012 Express. I am able to initialize from a snaphost. As well, any changes made at the main server, come down to the client fine, however if I make a change to a table on the Client, I get the error when I try to run the subscription to update.

Interestingly, I tested exactly the same setup, on a PC running a full version of SQL 2012, and it worked fine. 

The clients are not members of the server domain, and are connected via a VPN.

This is the relevant log info

TRAVERSESVR2\TRAVERSE11 is the main server

SDLLC13\TRAVTABLE is the Client

2014-08-19 00:08:03.425 OLE DB Subscriber 'SDLLC13\TRAVTABLET': {call sys.sp_MSadd_merge_history90 (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)}
2014-08-19 00:08:03.440 The merge process could not enumerate changes at the 'Subscriber'. When troubleshooting, restart the synchronization with verbose history logging and specify an output file to which to write.
2014-08-19 00:08:03.440 OLE DB Distributor 'TRAVERSESVR2\TRAVERSE11': {call sys.sp_MSadd_merge_history90 (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)}
2014-08-19 00:08:03.534 OLE DB Subscriber 'SDLLC13\TRAVTABLET': {call sp_MSmergeupdatelastsyncinfo (?,?,?)}
2014-08-19 00:08:03.597 OLE DB Subscriber 'SDLLC13\TRAVTABLET': {call sp_MSmergeupdatelastsyncinfo (?,?,?)}
2014-08-19 00:08:03.597 The Merge Agent was unable to update information about the last synchronization at the Subscriber. Ensure that the subscription exists at the Subscriber, and restart the Merge Agent. 
2014-08-19 00:08:03.597 OLE DB Publisher 'TRAVERSESVR2\TRAVERSE11': {call sp_MSmergeupdatelastsyncinfo (?,?,?)}
2014-08-19 00:08:03.597 The merge process was unable to update last synchronization information at the Publisher.

What should I be looking for here?