Service Unavailable when browsing CRM

After doing some configuration on CRM 4 server, i hit the "Service Unavailable" error when browsing CRM default homepage.

I am using CRM 64 bits version in windows 2003 with IIS6.
Problem cause by the IIS is not pointing to .NET framework v2.0 64bits anymore, since it is 32bits/64bits compatible. I suspect it default back to 32bits version.

Solution: What I did was open Command Prompt browse to [C:\Windows\Microsoft.NET\Framework64\v2.0.50727>] then do an "aspnet_regiis.exe -i" to register it back.

Work like charm for me.
Hope this help others who facing the same problem.