Editing deployment task causes deploy to fail

I run the SD management console on a VM & the images that I deploy are stored on a NAS device.

If I create a deployment task & create a deployment template all works well.

If afterwards I EDIT the template then the deployment fails: it stops at 3% and the target shows an error MBR error 1.

I wonder if this has anything to do with the image being stored on a NAS because if I CREATE a task then I'm asked for the userid & password for the NAS, if however I EDIT a task I'm not asked for a userid & password. Maybe these credentials are lost when you edit a task?

Anybody having any suggestions ?