Not prompted for username and password in order to save master image on network share

I downloaded the latest bootable image, made a boot cd, booted my hp elite and selected the option to create a master image. The first time I tried this I was able to provide the username and password of a user account of the pc where the network share is located. All went well until I got a lack of memory error message and the master image creation failed. I then made sure there was ample room on the share by deleting over 100 gigabytes of files. I then rebooted the hp pc, repeated the process to create a master image on the win 7 public folder share and this time I did not receive the prompt that allowed me to enter the username and password of an administrator account in order to be able to save the file. Does anyone have any idea whey I am not getting the prompt that allows me to provide credentials authorizing me access to the share?

Thanks