Array_keys() [function.array-keys]:

I’m a complete novice and have no idea what happened–tried to change some file names and received this error message (ErrorDocument 404 /index.php?error=404), so changed the file names back, but now on the wordpress dash, I have the following message:

array_keys() [function.array-keys]: The first argument should be an array in /home2/domain/public_html/wp-includes/theme.php on line 513

Is there something straightforward that I can do to fix this or should I installed WP through my shared host using Simple Scripts–should I uninstall it and try reinstalling it? Thanks very much!