Error: 'connection to specified xtuple erp server cannot be made'

This issue was raised in our forum, and we thought we'd post a possible answer here. We have spoken with various users who encountered this error and discovered something in common with both. Both had prior installs of other Open Source solutions on their computer, prior to installing PostBooks. In both cases the the other product also installed an instance of PostgreSQL. It appears the two installations of Postgres are conflicting, and preventing the PostBooks installer from finishing the install. If you are done for the moment evaluating the other Postgres-powered application, try uninstalling it, and then running the PostBooks installer again.