Unable to access SQL Server Express

I developed an Access 2010 application (.adp file) using SQL Server Express as the database. When I try to transfer the application and its database to another machine, I get the message "server not found." The target machine is running SQL Server Express, the database files have been attached, and the server is running. In the Data Link Properties dialog within Access on the target machine the server instance is listed, but when I choose it the server is not found. I notice, too, that the servier is not showing up over the network from my development machine (I can't connect to it in Microsoft SQL Server Managament Studio (MSSMS)). The server is up and connectable within MSSMS on the target machine. What may be causing me to be unable to connect to the server on the target machine?
[Later] I started a completely new Access 2010 project on the target machine. When I invoked the Data Link Properties dialog and clicked the Refresh button, 3 instances of SQL Ser ...