All of the above!
Your firewall should tell you if it's blocking Agwpe, check the log.
That Donner's interface is one I'm not familiar with, so it could be a problem. I'm assuming it's a USB thingy?
Make sure the sound card is getting a signal. You can check that easily with Agwpe by opening it, clicking on the port and then the little green square thingy in the top line. That opens the sound card/Agwpe 'level' window, check if the level is high enough or if there is one at all.
Post this same question on the Agwpe forum, sorry don't know the address off hand.
I don't know anything about that radio so read the manual about it's characteristics/abilities.
Ask George, SV2AGW if he has any suggestions, he's very helpful.
I can't say I've used Mixw with the Agwpe so checking all the port selections in Mixw and Agwpe isn't a bad idea.
If/when you figure out what's wrong, please post it, cuz I might run into the same thing.
Good luck.
- 'Doc