Same problem here... So I asked line 6 at Facebook. Here's their final answer. It worked for me. At least I get to download the HD pack, haven't had the time to install it yet..
"Hi. We're sorry you can't complete the purchase. Please go to Line6.com, then choose the globe icon in the upper right corner to choose "Netherlands". Once you do that, click on the "Store" link at the top of the page and you should be at shop.line6.com again. These actions should get the entire site into amode where it sees you as a non-US customer, allowing for the purchase. Please let us know the results."
