When I try to open the Yuletide Pack I got the error message: Sorry but this would put you over the treasure card limit.
So I sold off most of my treasure cards and tried again. then I got the error message: Sorry but this would put you over the reagent limit.
So I went through all my reagents and sold off 11 or so in all the stacks that were maxed at 999. Then I tried again to open the Yuletide pack, and now it is stuck on the same message: Sorry but this would put you over the reagent limit.
I'm guessing it is bugged and if you have a total of 999+ reagents (who doesn't?) then you can't open it.
Edit: got it to work. I must have missed one reagent when I was selling, so it is either checking to see if ANY reagent stack is at 999 or one that I missed like spider silk. Once ALL the stacks were less than 999 it worked.