Asus g51vx laptop cant change wallpaper

Hi guys,
I have an Asus G51Vx gaming laptop purchased from Best Buy a couple years ago. Since purchase its behaved flawlessly but now I've run into a problem: I can't change the wallpaper. I've done so many times in the past, so rather perplexed this is happening now seemingly without cause. I'm running Windows 7 Home Premium edition, so the starter-windows isn't the issue at all. The only thing I did different of late was to use an external monitor/kb/mouse for a time. I ran into this issue while using that external monitor, but its continuing now that I'm back to using the laptop's screen.

When I to change the wallpaper, whether from within the control panel interface, or just browsing to a picture, opening it in Windows Picture Viewer, then right-clicking and choosing 'Set as Desktop background', I get the following error message: This image can't be set as wallpaper. An internal error occurred.'

Any ideas/thoughts? robstuff36054[at]yahoo.com