You should try deleting your cache file to see if it clears up this issue. Here is a link to our document that details how to do this.
common_installation_issues.pdf
If you continue to have the problem there may be a corruption of your configuration folder. Here is a post that details how you can rename the folder to get past any problems associated with it:
showpost.php?p=12293&postcount=2
Let us know if you continue to experience this problem after trying these things.