I am having the same issue. I tried the intiall troubleshooting tips, didn't help. I tried unistalling and reinstalling the latest version, didn't help. I uninstalled the most recent shareware program i downloaded in case there was some conflict, didn't help. I defraged, checked for viruses, etc. didn't help. I tried over several days, in case the server was too busy. No luck. In fact, q-express runs just fine on my other computer if I try to download on it at the same time.
the debug log is:
ParseCommand Incoming command: "qxpress://qxfiles.modthesims2.com/qxpress.php?post=1706572"
ParseCommand qxfiles.modthesims2.com/qxpress.php?post=1706572
ParseCommand Getting QXpress file qxfiles.modthesims2.com/qxpress.php?post=1706572
ParseCommand Can't open http://qxfiles.modthesims2.com/qxpress.php?post=1706572

the only posts i've found said to try when the sever wasn't so busy, but since my crappier computer can download at the same time, i don't think that is the issue.