Time Machine not recognizing full space available on NAS.

I recently purchsed and set up an Iomega Storcenter ix4-200d NAS with Time Machine support. The NAS has 8 TB storage total, with ~4.6 TB available.

I have TIme Machine support turned on in the Storcenter, assigned to a folder called "Time-Machine." In my OSX Time Machine preferences, I select the "Time-Machine" folder on my NAS as the back-up disk, and my Mac connects to it just fine.

The challenge is Time Machine returns an error saying there isn't enough space on the backup disk to complete the backup.

For some reason, Time Machine is only recognizing 536.36 GB of space available on the backup disk, even though there are ~4.6 TB available. I tried manually moving my iTunes media folder (~700 GB) to the "Time-Machine" folder on my NAS to see if the Iomega NAS was arbitrarily setting a max size to a Time Machine folder. I was able to manually move just under 1 TB of data to the same "Time-Machine" folder that Time Machine says only has 536.36 GB of space.

I tried deleting the Time-Machine store on my NAS, turning Time Machine support off, then turning it back off and creating a new "Time-Machine" folder. I did this several times and still get the same behavior.

I even tried running Time Machine piecemeal, excluding larger folders at first and running a back-up, to see if maybe Time Machine wasn't liking that large of an initial backup. This worked, and then I gradually removed some exclusions and ran back-ups again, so each back-up size was never more than 200 GBs or so. However, after several back-ups, I received the same error message saying there wasn't enough space on the backup disk when the total sparsbundle size reached 536.36 GBs.

Since I can manually move more than 536.36 GB of data to the backup disk, I'm guessing it must be something with Time Machine not recognizing the full space available on the NAS.

Any ideas? Has anyone seen this before?