.NET Compact Framework 3.5 is supported by Rebex. The error you get seems to suggest that you are trying to reference some incompatible assembly (i.e. assemlby targetting a different platform.)
Could you please try one more time and make sure you reference assemblies from the "netcf-3.5" folder installed on your computer?
The path to the .NET CF 3.5 compatible Rebex libraries is:
"%Rebex installation path%\Rebex Components\bin\netcf-3.5"
Please give it a try and let me know whether it works now.
BTW, we also offer samples targetting VS 2008 and .NET CF 3.5 that get installed along Rebex components. You can find them on your computer at:
"%Rebex installation path%\Rebex Components\samples\source\vs2008-netcf-3.5
So you can give them a try as well.