Unable to deploy image to a Wyse Terminal via WDM

I have created a new Z90Q7 image from the latest available Build for WIN7, when pushing the image via WDM I get the following error:

Try 1:Merlin-Process-FAILURE [Thu Aug 11 15:09:55 2016][ERROR: Error while uploading MBR file. Http Error code : .][ERROR STAGE: MBR

validation.][REASON: Flash is corrupted or improper repository/network

configuration.][SOLUTION: Disable anonymous authentication if enabled on software repository under MyWDM virtual directory or check the device flash.] 

The image does install on the device when pushing from a USB pen.