Concurrent Publishing error is issued in the following situation:
Your module is currently being locked by another operation. Please try again later. User <user> is publishing module <module> (in Personal Area) since <date/time>
It can be one the following situations:
You are trying to Run the module in your Personal Area while a 1-Click Publish is being processed in the server or another developer with your credentials is also updating your Personal Area.
You are trying to execute the 1-Click Publish operation while a Run is being processed in the server or another developer is also publishing the module.
Wait a few moments and try the operation again.