This would usually indicate that the connection string in the messaging.config for the On-Screen TakeOff application is malformed. The most common issue is that there is a space somewhere in this.
The file is found in the root of the application install directory, which is usually C:\Program Files\Conquest\On-Screen Takeoff
Ensure that the connection string appears in the following format, with no spaces between the double quotes:
<property name="connectionstring" value="amqp://username:password@server:5672//" />