VLK, Retail,OEM etc are detemined by the setup media files (OEMBIOS.*,setupp.ini,PIDGEN.DLL and "Product Type" key in txtsetup.sif,setupre.hiv) once installed setup creates various confs in registry according to these Tweaknt/NTswitch chages them apparently "Windows Activation" check routine in winlogon verifies and locks these setting at every logon. A VLK system need no activation, all others need that. So converting VLK to any other need the system to be activated. This checks by winlogon fails and u cannot logon. To solve this either us a Retail version or a crack (ILLEGAL) to bypass winlogon check. PS: TweakNT is considered as a Warez (MSFN W2K3 to workstation guide) if xpconv also do the same it too.