In our farm we have the following issue: Created a workflow with a few easy steps. The first step is a "assign a variable" step, all following steps are within an impersonation step. That workflow works about 7-10 days, after that all new workflows stops after the first step just before the impersonation step. The workflow history displays: "Canceled" by "System Account" without any more info. The ULS log shows nothing regarding workflows (log level is set to "High", because it is a production environment).
Any ideas, what could cause the workflow stop working after a few days within the impersonation step?