I was spending a lot of zerocoins over a period of time and all of a sudden I got an error message saying "Mint did not make it into blockchain" and the spend failed. Every subsequent attempt failed, even after waiting several minutes.


The solution was to do: 

rescanzerocoinwallet

and then try a few minutes later.

This fixed it, no problem. I did many spends after that without error. Whenever I do `rescanzerocoinwallet` I do prefer also to do `rescanringctwallet` before it, which normally takes no more than a few seconds.