On a Windows XP SP2 + patches OS, the xtInfoPlugin functions GetDotNetFrameworkId and GetDotNetFrameworkVersion returns 2.0 and 2.0.0 respectively on a fresh system with clean, fresh install of .Net framework 3.5 (downloaded from Microsoft web-site. Useing NSIS 2.46 (most recent download) and xtInfoPlugin v1.0.0.2 (downloaded fresh). Screen-shot shows entries from DetailPrint and Installed Programs list. Problem is not confined to one machine or XP installation.
Script lines were:
xtnfoPlugin::GetDotNetFrameworkID
Pop $0
DetailPrint $0
Screen-shot of version test result.
This is not one of the official plug-ins packed with NSIS. You should contact the author of the plug-in for help.
I seem to recall something about .NET 3.5 being v2 with some more packages that have to do with GUI. But I'm by far not a .NET expert...