Uploaded file is only 1 byte

When I try to upload a file in a new install of 2.5.1 it appears to be successful, but no thumb image shows up in the flash viewer. Three files are created in the proper directory (original, thumb size, and medium)with the right extension (.jpg in this case) but if I download those files I can not open them in an editor and if I check the properties the file is said to be 1 byte. Any ideas?