You could try probably right-click on the file go to properties. Then click on Security tab. There you can finding rules for System, owner, groups etc. So you could try change the read-only property there.
My newest HP desktop computer I got with Windows 7 installed. At one point that computer became "read only". I discovered this when I tried to save a picture in my picture folder. I learned the folder was "read only". In Google I found a couple lightweight attribute changers but the read-only persisted. Does anybody know how to fix this ????