Cisco pix 515e not enough space

I am setting up PDM 3.4 on my pix 515e. My issue arises when I issue the copy command, and it almost immediately says that there is not enough space.

pix-515e-01(config)# dir

Directory of flash:/

9 -rw- 8515584 23:53:09 Dec 05 2009 pix724.bin
10 -rw- 5166 20:57:00 Oct 05 2009 cisco-config-final

16128000 bytes total (7596032 bytes free)

So, I should have ~7.5MB of free space, out of the total 16MB

When I issue

pix-515e-01(config)# copy tftp://172.16.1.101/pdm304.bin flashdm

Address or name of remote host [172.16.1.101]?

Source filename [pdm304.bin]?

Destination filename [pdm]?

Accessing tftp://172.16.1.101/pdm304.bin...!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
%Error copying tftp://172.16.1.101/pdm304.bin (Not enough space on device)

The file is 3MB, so I should have enough space. The security level of the interface is 100. Not sure what else I can do, or how to figure this out?

Thanks a ton!