You should try deleting your cache file to see if this helps resolve the problem, here are the steps you can take for this:
common_installation_issues.pdf
If you still have this issue after performing these steps then it is possible that you have a corruption of your configuration folder. Here are the steps you can take for that:
showpost.php?p=12293&postcount=2
If this issue persists please let us know and I will ensure that a ticket is opened for you.