Have you tried deleting the cache file? If not this is the first thing you should do, here is a link to the instructions for this:
If this does not work then there might be a problem with the configuration folder. If this is the case you will need to rename or delete this folder to have it be recreated, here is a link to the steps that you can take for this:
If you continue to have problems after trying these things please let me know and I will ensure that a free ticket is opened up for you.