It's of absolutely no consequence, merely my innate insatiable curiosity. I meant read only attribute is checked in windows properties is all. Sorry for the 'red herring':
PS: I found it was read only because i wanted to check both images in BaseCamp before using in the SP but test_original.img wasn't visible because of MS flag '1'. ImgTool showed it as 'read only' when i opened it to change the flag.