Cannot connect to SQL Server 2008 R2 installed on Win Server 2008 R2 in domain controlled by Win SBS 2008. Get "Server doesn't exist ..." message

I have 2 SQL Server 2008 R2 instances installed on a new server running Win Server 2008 R2 in a Windows SBS 2008 domain.

The instances are configured to allow remote connection. The users are authorized in the SQL root security. The users are authorized for the computer and both SQL instances. Shared folders on the computer are visible remotely.

When I attempt to connect to either instance either programmatically, or using SQL Server Management Studio, the attempt fails with a Server not found ... error. I cannot see either instance.

I opened port 1434 in the firewall but that only made things worse.

I have not experienced this error before in SQL Servers 2000 or 2005.

Can anyone tell me what I am doing wrong?

Thanks.

Murray