So you have a SQL Server and all but one machine can connect to it?
Okay, how does the application connect to the SQL Server? Does it use an existing ODBC connection? If so, you can take a look by Start | Control Panel | Administrative Tools | Data Sources (ODBC). If it does, compare the settings for the ODBC connection on a working system versus the broken one.
There are a few other areas that can be checked, but how the app connects is needed.
K. Brian Kelley
@kbriankelley