If doing a simple restart of your machine does not do the trick then you may need to delete this cache file to make use of the tool. Here is a link to the instructions for this:
common_installation_issues.pdf
If you do this and still have the problem you should try deleting this file again and restarting your machine before trying to use the tool after this.
If the problem does not go away it may be due to some corruption of your configuration folder, here is a link to a post with the steps you can take to rename this folder if this is the problem:
showpost.php?p=12293&postcount=2
