I have the same issue, my project is working on Windows (just a static ground with a dynamic box), and when I try to run it on Xbox, it crashes with an Error 4.
Guys on the XNA forum said a few interesting things :
http://forums.xna.com/forums/p/25876/141383.aspxI'm not really an expert when it comes to dll, but one question remains :
Can you release a dll that will work with the xbox, or it is hopeless ? Or did we do something wrong

?
Some more information on the crash :
Quote:
An unhandled exception of type 'System.MissingMethodException' occurred in Box2DX.dll
Additional information: The version of the assembly System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089 cannot be loaded by this version of the Microsoft .NET Compact Framework.
Happens at this line :
Code:
worldPhysic = new World(worldAABB, new Vec2(0.0f, 10.0f), false);
!