Time Machine Problem

I have been using a Iomega ix2 NAS with Time Machine with no problem. I ran out of space on my ix2 NAS so I upgraded to a ix4 NAS with much more capacity. I removed the old backup disk from Time Machine and added the new backup disk with no problem. When it goes to backup I get the same message that I don't have enough space (as if it was still going to the old ix2 device) even though it shows plenty of free space on the new drive. Does Time Machine keep some type of local files on the Mac that it is referencing when it goes to do a backup?