weird disk error - aix

Hi,

Once or twice a day, I get the disk test on ONE of my AIX boxes go red. When
I look at it, it says:

Expected string (%Used and Mounted) not found in df output header
realmem 1048576 Amount of usable physical memory in Kbytes False

The next cycle (5 minutes) it goes right back to being green with the
correct data.
This happens once or twice a day.

Any ideas?