When attempting to connect to SQL server database using Dynamics NAV SQL client, you may recieve the following message:

The Server cannot be found. Try again later or contact your system administrator.

System Environment:

Server: Windows Server 2008 (any edition)

SQL Server: Microsoft SQL Server 2008 (any edition)

Dynamics NAV: 2009 SP1

A solution on how to open the firwall port can be obtained fromthe following  Microsoft Knowledge base article:

http://support.microsoft.com/kb/968872

Hope you find this helpful