Shadowing or caching of BIOS memory is a setting in your BIOS that allows using some of your system's RAM to cache BIOS code. It may offer better system performance providing RAM access speed is faster than your BIOS' ROM. When you do that, it reduces the amount of memory available for running programs. The error message is telling you to disable the caching in order to free up memory.
If you didn't recently turn that option on in your BIOS settings then I would suspect that some portion of your RAM has gone bad and reduced the amount of available RAM in your system.
Edited by strolln, 04 July 2010 - 05:22 PM.