Hopefully someone from Line 6 will be able to get things going for you...

In the meantime, I have an early hd400 that has a channel D button that will do that from time to time...I have never repaired it because there is a little workaround that has worked for me for i think over 3 years now...spin the button about 90 degrees...It seems, at least with mine, that there is a little rough spot on the button shaft and when it gets in this one certain position, sometimes it won't stick...Not saying your issue is like mine...just offering a little workaround that might get you by until you can get things rolling with Line 6 support...On that note, have tried using a different computer or browser to submit your ticket? I have less trouble with the support site using the Google Chrome browser...wierd stuff in Firefox and IE...