This occur only on one workflow. It is reproducible on demand.
There are no other errors while running the workflow other than "The "Variable" action is not available with the currently registered license key."
My workflow contain only get service and stop and start serivce,below are the sample code in the task
<AMVARIABLE NAME="Var_TT" VALUE="" />
<AMSERVICES ACTIVITY="state" SERVICE="AutoMate BPA Server 10 Agent" RESULTVARIABLE="Var_TT" />