You may possibly have a dodgey connection via the cable from your E-trac, through to the usb connection or the usb port may not functioning properly. Try another usb port.
Some info here:
http://www.computerhope.com/issues/ch000726.htm
or
If it's software related, maybe uninstall E-trac Xchange and re install it. If that fails and assuming you are using a Windows PC ,you may want to engage Microsoft Security Essential and/or use the online MS FIX it center to help out with any problems with software.
I am sure that you're aware that the detector needs to be switched on while your doing this pattern download through E-trac Xchange. I tried "download all patterns for E-trac" without connecting to my E-trac and it reports:
"Could not connect to the E-trac. Check the connection and try again."
I'm using windows 7 and tried it on vista and xp. They all work fine and report the same when E-trac is NOT switched on.
Hope I've helped.
daviddi