It looks like you have selected to limit the availability to the user rule selected in the interface. This means that you will not be able to upload unless you pass this rule. Do you use this rule on any other pages in your admin area? You must ensure that you are passing this rule before you will be able to use the upload feature.
As a test of this you can try changing it to everyone then upload and test it. If it is set to everyone then you should have access regardless of the rules you pass. If you have the same result then the issue is probably not related to the access rule. If this is the case please post back and include your HTML editor folder in a zip archive attached to your reply.
