Is Windows Server 2003 updated to SP2?
The 2003 is win2003 x64 5.2.3790 R2 Service Pack 2
You got the error when running Classic Client or RTC?
i got the error when running RTC
How NAV has been installed? If .msi file was used it's possible that .NET framework hasn't been installed. In this case, try repairing the installation with the autorun executed with "Run as administrator" option.
I forgot how i installed, U mean i should uninstalled and then install again?