Permissions denied on Full Size image file

I administer two WordPress applications on my website on a Windows 2008 server using IIS7. When I load an image through the admin console, four files are created in the wp-content\uploads folder. Three files are for the Thumbnail, Medium, and Large images with the dimensions of the image added to the file name. I can access these just fine, but the “Full Size” image file (the one with the same file name as the original) can not be accessed due to permissions being denied.

I have gone into the server and opened up the permissions for all users (even adding in the “IIS_IUSRS” group) by giving them full control (at least until I can fix this). When I do this, the full size images then can be seen in the post, but any new image files added afterward have the same permission restrictions and are not viewable.

I also tried changing line 42 of the wp-admin\includes\class-wp-filesystem-direct.php file from:

$this->chmod($file,$mode); to $this->chmod($file,0774);

That didn’t do it either. Upgrading to the latest version is an obvious option, but I hestitate to that since I have only been administering these applications for only two months and I am afraid I won’t be able to figure out any issues that arise from the upgrade.

Does anyone know a quick hack to get around the permissions issue that I can put into place before I make the upgrade?