I tried both of those tips based on Google searching, and also cleared out the cache for the download manager, and neither worked. I eventually just deleted the email because I got sick of it saying sending. As for the app, the app I am trying to download is GameBoid, does that maybe not work with the X?
This happens to me, too. When it says "sending..." I go to menu -> back to inbox and then when I'm in the inbox I go to menu -> refresh and it has sent. Kind of roundabout, and shouldn't have to do it, but at least it sends it.
Somehow the autosync was turned off. Here's what I found on another site:
First select your gmail icon, then hit your options button and select accounts. On top should be the envelope with the gmail written next to it underneath should be your gmail account. Next, hit your option key again and seletct account settings. There should be a Background data checked green and underneath is Auto-sync. Make sure that is checked green. Mine wasnt and after highlighting that option, the section beneath labeled "Manage accounts" switched to Sync is ON with a grean circle (refresh symbol) appearing.
This fixed the sending problem for me, as well as not telling me about new emails. Thanks for the help!