Acronis 2012 Sync is no longer syncing

I've just started using Sync. It worked fine but has now stuck. The log says it has sync, but it's not done all the folders, and the green bar is stuck a quarter of the way along.

I am syncing to a USB drive on my router. It is doing a smaller sync to another folder on the routers USB drive without any problem.

Any suggestions how I fix this much appreciated,

Dazzer