This error means that the dbFront Web Application attempted to talk to the dbFront Service and received an invalid response.
The most likely reason is that there was already something else installed to use that port.
When the dbFront Web Application and Service talk to each other they use a default port number. The default port number was originally port: 8080. For new installations of dbFront, the default port has been changed to port: 42057.
To view what ports are in use on a server you can run the following from an Administrator prompt:
To check the default port number and change them if needed you can see: