but the is_readable function returns that it is readable

wait a minute, did the original code do that as well?

Like I said earlier, newer versions of windows can have files which stat like readable but it won't let you read them (this is normal)

-r doesn't check for these things (this is normal)

you have to check for these things ... I've never dealt with this ... the win32api docs explain some of it as does tye :)
(tye)Re: Opening a locked file for reading
(tye)Re: Unable to write to a file opened in read only mode
http://live.sysinternals.com/handle.exe and http://live.sysinternals.com/procexp.exe can help you see some diagnostic stuff

If you SetErrorMode to 2 you won't get error popups that interrupt the program (but you won't be able to read file either)
if you use cacls you can see or change the ACL (permissions) if that is a problem

Good luck