Warning when referencing DLL library

Apr 5 at 6:42 PM
I have a console application done in Visual Studio 2008 Professional and .NET Framework 3.5. I have downloaded current package in this web, 1.9.71.2 stable. When I reference library from "\libcmdline-1.9.71.2-stable.zip\CommandLine\src\libcmdline\bin\Release" into my .NET Framework 3.5 project in Visual Studio 2008 Professional I get a warning icon. The error says:

"Resolved file has a bad image, no metadata, or is otherwise inaccessible. Cannot load neither file or assembly "c:....\CommandLine.dll" nor one of its dependencies. This assembly is built by a runtime newer than the currently loaded runtime and cannot be loaded"

As far as I know, it is said that this version is compatible with .NET Framework 3.5+ so I understand .NET 3.5 is included in the list of compatibility.

Please, help.