Form failure: <startForm> <- Cannot get start form data for process definition messageTask:31:d713968f-23a2-11e9-b4d5-e82a44d20265

Hi guys !
im trying to start a process and it produce this error " Form failure: <startForm> ← Cannot get start form data for process definition messageTask:31:d713968f-23a2-11e9-b4d5-e82a44d20265"
i have two process with message events process.bpmn (9.7 KB)
like in this diagram if i start the process withMessageTask A this flow works fine …but when i start the poolB process alone i get the above error … If i delete the signal start event process PoolB works just fine …can someone help me what i am missing here…thanks a lot

How did you solve this?