Have you tried using a regular USB cable?

If your version is 2.x or higher you do not need a midi to usb.

At the bottom of this doc are instructions on how to determine your version.

http://line6.com/support/docs/DOC-3827

Also make sure you have the newest Monkey and drivers for your OS.

http://line6.com/software/

You can also use Gearbox instead of Edit with the PODxt.

Plug the XT into your PC from the USB port of POD (the printer jack end) and plug the other into USB port of desktop.  Make sure Monkey is installed.  Line 6 edit should work fine afterwards.  Make sure the XT is switched on before openning LIne 6 edit.  Then with Line 6 edit you can find and edit all your new tones and then use the save button on the xt itself into whichever bank you have chosen.

https://www.youtube.com/watch?v=niAvK37ckeM