Problem Reaching VM SQL Server Instance Here's what I'm working with right now.  I have a host OS which includes a SQL Server 2008 Enterprise instance.  I have a virtual machine running on this host which has a SQL Server 2008 R2 Express instance.  In the virtual machine, I can connect to the host instance in SSMS.  But in the host OS I cannot reach the virtual machine's Express instance.

What could be causing this?  The host can ping the virtual machine, so I don't think it's a network issue.  And in the SSCM on the virtual machine I have set the appropriate network protocols enabled.

Any other things I need to look out for?
In order of what to try:

1. Enable TCP/IP

Go to: SQL Server Configuration Manager on your SQL Server VM, under SQL Server Network Configuration choose your instance (should be Protocols for SQL2008), enable your preferred protocol (I'd guess TCP/IP) and give it another test.

As to why it's usually disabled:

From MSDN article:


  For security reasons, networking protocols are disabled by default in
  SQL Server Express. Individual protocols can be enabled manually or
  during installation of SQL Server Express.




2. Start SQL Server Browser

Go to: SQL Server Configuration Manager on your SQL Server VM, under SQL Server Services make sure SQL Server Browser is running.

from MSDN article:


  SQL Server Browser is used by some networking protocols to associate named instances with  TCP/IP port numbers. However, if SQL Server Express is installed on the same computer as a pre-SP3 version of MSDE or SQL Server 2000, there might be conflicts. Also, the SQL Server Browser service does not start automatically after installation




3. Check your instance name

If you install SQL 2008 Express (or later versions), the Server instance will be named as SQLExpress, so to connect you will need to specify ServerName and InstanceName, ie:

[VMServer\SQLExpress]




4. Check Connection on SQL Server

In SSMS on Server right click Server, go to Connections and make sure that Allow remote connections to this server is checked



5. Basic network checks


Create a folder on your server, share it and make sure you can see it from the other machine.
Try to telnet to it
netstat -ab




Security
You might run into authentication issues, but that should be a straight forward matter of adding your user onto the SQL Server instance.

Note: If none of the above work for you, and you find the solution, please add your solution to the list above (trying to help future users as well)