If you are getting a "Request File Could Not be Found" error then please see the following post first and make sure none of the issues stated there are happening:
http://www.tipsandtricks-hq.com/forum/topic/downloaded-file-size-is-0-zero-byte
If the above post doesn't solve the problem then try the following:
Go to the "AddOn Settings" tab from the eStore's settings menu and check the "Automatically Convert to Relative URL" field.
If you are still having an issue after that then please let us know and we will take a look.