Lately whenever I try to vend I keep getting the same message:

The vending key (dedro/frore) is invalid! Please follow the link below to return.

The words in the brackets keep changing, but it occurs at least half the time whenever I click. I'm not sure if I'm doing something wrong or if it's me, but it's really frustrating. Any ideas on what it could be?

edit: Woops nevermind! Missed a very similar thread on this same topic. Sorry ): You can lock/delete/whatever this