Firewall – Application Unable connect Remote Server. FIREWALL Issue

Probably you forgot to execute this command:

 netsh firewall set portopening TCP 1433 "SQLServer" 

You could try out the new "Fix it" feature of this Microsoft support article: How do I open the firewall port for SQL Server on Windows Server 2008?

The page also contains a script, delete the lines, if you don't need SQL Service Broker, debugger, https etc.

@echo =========  SQL Server Ports  ===================
@echo Enabling SQLServer default instance port 1433
netsh firewall set portopening TCP 1433 "SQLServer" 
@echo Enabling Dedicated Admin Connection port 1434
netsh firewall set portopening TCP 1434 "SQL Admin Connection" 

...

netsh firewall set portopening UDP 1434 "SQL Browser" 
@echo Allowing multicast broadcast response on UDP (Browser Service Enumerations OK)
netsh firewall set multicastbroadcastresponse ENABLE 

You can disable Windows Firewall using the Registry; the relevant settings are in

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\SharedAccess\Parameters\FirewallPolicy

Under there, you will find three keys: DomainProfile, PublicProfile and StandardProfile; each of them contains a value called EnableFirewall, which controls the firewall state for that profile. If you set all three values to 0, Windows Firewall will be completely disabled.

If you want to do this for an offline system, you'll need to load that system's Registry into Regedit; the file to load is C:\Windows\System32\config\SYSTEM. You'll also need to find the right ControlSet to configure, because CurrentControlSet is only available at runtime; when operating on an offline Registry, you'll need to choose the correct one between the various ControlSet00x you'll find under HKEY_LOCAL_MACHINE\SYSTEM. HKEY_LOCAL_MACHINE\SYSTEM\Select can help you here.