In Windows 2008 the Guest account diasbled by default.
No matter what permissions i gave a share or NTFS permissions on the folder, I could not access it without a login prompt.
Users were crossing from a (deliberately) untrusted domain on a separate network.
I don't use anonymous access usually, but this was just as a file store.
It was resolved by >
Enabling the guest account on Windows 2008
* Computer Management > Local Users and Groups > Users
* Right click Guest > Properties
* Untick "Account is disabled"