Unity3D removing project references in MonoDevellop

Hey, I am trying to use Mono.Data.Sqlite in my Assembly-CSharp-firstpass project. In MonoDevellop, I right click on the project, edit references, and add Mono.Data.Sqlite to the references. If I build from Mono, everything goes smoothly and and no errors are produced. When I move back to Unity3D, I always get the error saying that Mono.Data.Sqlite cannot be found. If I then close Unity + Mono and reopen both, the reference to Mono.Data.Sqlite is gone! Anyone know what is going on?