Why does the download test work, but the upload test does not?
This most often is the result of software on your computer that is filtering traffic between the web browser and the server. Examples of this are firewall software such as McAfee, Symantec or Zone Alarm. Temporarily disabling the firewall will solve the problem. Speedplexer Inc. recommends closely looking at the firewalls properties and modifying the settings so that Speedplexer will work with the firewall enabled.