How exactly is your Admin rule defined? If it is based on a variable and the value is not available or the value is not matching the rule will restrict access.
As a test of this you should try printing out the value that your rule uses on the page to determine what this value is when you are denied as well as when you logout and gain access. You should put this on the page you are logging out with so you can see it before and after you logout. When you test it bring up the browse server interface, open your new window and check what the value of the variable is, then go and try to upload. This should fail, then do it again but logout this time and confirm the value of the variable.
Please get back to us with what you discover, if you have any questions about any part of this please let us know.