Just throwing my 2 cents in...it worked fine for me when I first tried it shortly after it was announced. I was using Chrome and had no issues with the whole process.
Thanks for the heads up, I was using IE 10 when I was trying to transfer my team over with no luck, my teammates still can't get anywhere as well with the invite links.
The minute I read "IE" I got shivers . If you choose to bypass the import I'm not sure there is a way to ever get that option back. From my understanding it is a one time option. As for why the link doesn't work, make sure you have the clan set to allow applications. If that is set and it still doesn't work, you may want to try and contact Activision so they can pass it on to Beachhead to investigate. I'm beginning to think there are going to be "cursed" clans just like there were in Elite where some clans couldn't remove members, etc. Not trying to cause panic, just stating an observation...it is developed by the same developers after all.
Makes sense now why it's not working... Beachhead is still developing elite. I was back here talking to Activision support back in 2011, they told me to try it on Chrome and FF as well. Looks like something's never change, and can you believe I actually paid for a broken service back in 2011? At least it's free today, and still broken.
My friends have all tried accepting the invitation links on their PC's, laptops, iPads, mobile devices with no luck.