For whatever reason IIS likes to set the default version of .NET on some versions of IIS to 2.0. This is generally rediculous since 4.0 has been around for some time and even when 4.0 is installed and working, MS will default to 2.0.
If you install Lucee server on to your windows server and get this error, there are several possible causes:
1) You need to use a more recent version of .NET for your application pool. The fix is to adjust your .NET application pool version to 4.0 (or above) for that site, then restart the pool. Once you do that, your Lucee install should work perfectly.
2) You need to ensure that you have .NET Extensibility turned on in your IIS Install. In windows 7, this is what the window looks like:
3) You have a .NET version cconflict. You'll need to remove all versions of .NET from your machine and re-install Lucee to let the installer handle installing .NET.
Hope this helps!