“Failed to lock variable” SSIS error

Question

I am getting an error randomly for a scheduled SSIS package which runs hourly. The funniest thing is that if I delete the checkpoint file and run the package again it works

Answer 1

Another variation of this error: I copied a task from one package to another package. The task contained parameter mappings, but the source variable was not available in the new package. This made the parameter mapping invalid.