I have a strange issue that believe to be permissions. I f

HI Guys I have a strange issue that believe to be permissions.

I f i upload an image it is broken and if i view via url it throws a 500 error i thought this may be down to the rewrite rule but it appears that if i alter the broken image in any way it appears also if i update the files permissions directly from windows it works??

The permissions seem to be fine i just dont understand why it wont work straignt from the upload?

Thanks