How to configure SQL 2008 R2 Express to allow remote machine to connect to it

I'm building a new XenApp 6.5 Farm, which requires SQL 2008 R2 Express(which I've installed on a machine called vCitrixServices). I installed XenApp on vCitrix1 and started to creating a new farm, but I get this error trying to connect to our database.

DB server : vCitrixServices

I can connect using MS SQL Management Studio on the DB server using just the server name. (The SQL Server Service says the instance is called MSSQLSERVER)

I tried on my machine with Navicat Premium, and I get this error.

Things I tried that didn't work :

• All the services are enabled (SQL Server/SQL Server Browser and Client Protocols[ TCP/IP, Named Pipes, VIA])

• Remote connection were enabled.

• Added rules to windows firewall on vCitrixServices(and even turned it off altogether)

• checked all network connection from vCitrix1 and my machine, no problems there.

• Ran cliconfg.exe, and Named Pipes & TCP/IP are both enabled with priority to Named Pipes

• Named Pipes had a default pipe of "sql\query" Couldn't find if that was a problem or not.

• Client Tools & DB Engine were installed. (https://stackoverflow.com/questions/360141/how-to-connect-to-local-instance-of-sql-server-2008-express)

I've done a few more things, but don't remember them all… I'll update the question with the results of any new test.