I am interning at an organization that has two exchange 2007 servers. They both have Windows Server 2003 R2 x64 installed and as far as I am aware are identical. One is able to use NTbackup just fine while the other cannot perform backups. I havent been given any other information about the servers, I am just wondering if there are any known backup issues or general fixes I can try. The backup does run but it does not backup any of the mailbox files. when the backup is done the file shows up but it is only 2kb large.

You need to look at the backup logs that are created. With out any more information, all I can say is make sure you know that ntbackup cannot backup a remote Exchange server. you would need to run two seperate backups, one on each server. Using Backup to Back Up and Restore Exchange Data http://technet.microsoft.com/en-us/library/aa998870.aspx