WebFile URL Blank

I am trying to download a file from a SQLIte database and have it opened on the client automatically. The file is a powerpoint presentation. The blob read is done in a thread. Once the thread has completed successfully I fire off a completion event (passing the file data). The completion event then loads the data into a previously instantiated WebFile (attached to a container that lives throughout the entire process) and attempts to invoke the ShowURL method. The problem I am encountering is the URL field of the web file is empty. When ShowURL is invoked with an empty field it appears to restart the web session. I have set the file name, mime type correctly and have set ForceDownload to true.

Any help would be greatly appreciated.