Mono.TextEditor not working. What am I doing Wrong?

I am trying to use the Mono.TextEditor assembly with .NET Framework 3.5 in GTK#. But I keep getting System.BadImageFormatException

Could not load file or assembly 'Mono.TextEditor, Version 开发者_运维知识库= 1.0.0.0,Culture = neutral, 
PublicKey Token = null' or one of its dependencies. This assembly is built by a runtime
newer than the currently loaded runtime and cannot be loaded.

The MonoDevelop version I am using (Mono.TextEditor is an addon of MonoDevelop) is definitely built by .NET version 3.5. Any Help?

Most possibly your project still targets the 2.0 runtime. You'll need to set Project/Settings/Build General/Runtime: Mono / .Net 3.5 in monodevelop.

Don't forget to add the reference to System.Core, if it isn't already added.