[CentOS] GDM problem

Hello,

Went to login to the console this morning and got few errors about bad 
PNG files.  Logged out, now I can't log back in.  The lone dialog box 
has the following:

There was an error loading the theme Default
Couldn't recognize the image file format for file 
'/usr/share/gdm/themes/Default/background.png'

I click OK, nothing happens.

Suggestions anyone?  Thanks!