VCO stopped flow execution

We are facing an issue in VCO, VCO flow execution stopped with message "Error..." with no exception details.

This issue is happening in an erratic manner, and happening at different locations on any flows. Attached screen shot. Have any one faced this issue,  How to resolve this issue.

VCenter Orchestrator version           5.1.0

Build Number                                 2725

Thank you so much.