A message flow that specifies "Use map in project" displays the error "Could not open map" when you deploy the message flow to an execution group without building and deploying a broker archive (BAR) file.
When you deploy a flow without building a BAR file, WebSphere Transformation Extender is not called to build a map archive (MAR) file. The message flow is deployed without any maps.
Resolving the problem
With WebSphere Message Broker V126.96.36.199 and later releases, always build and deploy a BAR file before you deploy a message flow that uses the "Use map from project" setting for a WebSphere Transformation Extender map.