Comment 12 for bug 478761

I just had difficulties to scan on a network-connected Brother MFC-5440CN after the Upgrade from Jaunty 9.04 to Kamic 9.10. Updated the brscan2 driver, added it to the configuration and it worked.
So far so good, BUT when I wanted to test it the first time, I executed "scanimage -d brother2:net1;dev0 --test", which gave me the same error you had above:
scanimage: open of device brother2:net1 failed: Invalid argument
dev0: command not found

It was just that the shell interpreted the semicolon, but maybe interpretation of the device name is the source of your problem?
Hope this was helpful.