Deployment errors can be hard to track down when they give vague descriptions like when a Process Builder encounters an error. You end up with something like this.
System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_EXECUTE_FLOW_TRIGGER, The record couldn’t be saved because it failed to trigger a flow. A flow trigger failed to execute the flow with version ID 30121000000UF54. Flow error messages: An unhandled fault has occurred in this flow
An unhandled fault has occurred while processing the flow. Please contact your system administrator for more information. Contact your administrator for help.: []
To figure out what ‘30121000000UF54’ is, the Id can be opened in the Flow designer. Enter the url for the flow designer with the Process Builder id, and the name of the process builder will appear at the top of the page.
// format
https://{node}.salesforce.com/designer/designer.apexp#Id={ProcessBuilderId}
// example
https://na1.salesforce.com/designer/designer.apexp#Id=30121000000UF54