Exception from HRESULT: 0x8102009B
Turns out this occurs if there is a prior instance of the same workflow which has terminated in an error, showing a status of ‘Error Occurred’. (This would be true if you were trying to invoke the workflow from code as well.) Through the UI, you can remedy this by going to the item and terminating the workflow instance which resulted in an error. I don’t think that there is a fix available through the Workflow Web Service. In code, you can call the CancelWorkflow method.