Have you tried deleting your cache file? Here is a link with steps you can take for this:
common_installation_issues.pdf
If you continue to have problems with this there may be a corruption of your configuration folder, here is another link with steps you can take to deal with this.
showpost.php?p=12293&postcount=2
If you have tried these things and still have this issue please let us know and I will ensure that a ticket is opened for you on this issue.