I've just had the same experience; the block was removed after a little while. I submitted the report, and I think the subsequent screen explained that Zazzle were trialing some new security measures.
They are fighting the recent wave of bots I guess, which is great, but I hope they solve this issue because it's affecting us, I can't create new products without getting blocked then closing and reopening my browser..
After receiving the same error, I tried logging in on a new incognito tab to bypass cookies. Once that succeeded, I switched back to the regular browser window and, miraculously, I was logged in there as well.
