I had the same problem on one of my netviews , i checked the background
files and found out that i had two files with different sizes from my
other netview-system.
After i had copied the good files over the corrupt ones , the message
disappeared .
Probably something went wrong when you copied this files from CD in the
installation process.
Try to restore an older version of your background-files or delete the
corrupt files , if you don't need them and if you can find out which one
is causing the problem .