Unable to Deploy any Apps to Wyse Clients

I'm unable to deploy any apps to Wyse Clients (all Win10 IoT). 

I've added the app to the repository, created a policy and applied it, but i receive the error -

Failed - Download_Failed(Protocol Error : EXCEPTION)

I've tried to download the latest command monitor and Microsoft Remote desktop both give me the same issue.

The device will register fine (using DHCP) and update & configure, but will not download new apps.

I cant find any references to Error messages on the Dell Wyse Management site, which seems a bit limited.