I get an OS Loader Lock error
It is not an error, it is a warning. From an MDA, a Managed Debugger Assistant. They are little slivers of code that Microsoft inserted into the CLR and the debugger to produce warnings when it looks like your program is doing something wrong. The kind that doesn't produce an exception but makes your program hang-up or fail in a very difficult to diagnose way.
Loader lock certainly fits that pattern, it is a deadlock buried inside Windows internals. Associated with the loader, the part of the operating system that's responsible for loading DLLs and calling their DllMain() entrypoint. It takes an internal lock to ensure that the DllMain() functions are called one-at-a-time. It prevents re-entrancy problems, pretty comparable to the kind of trouble Application.DoEvents() causes. A deadlock on that lock is pretty hard to debug, the code is completely buried inside operating system as well as mysterious DllMain() functions you don't know anything about. Very high odds that a real deadlock would get you to tear your head-hair out in major clumps with little to show for it than a bald spot without that MDA.
Unfortunately the MDA tends to produce false warnings. It is not always aware that deadlock cannot actually happen. It is over-eager, a side-effect of it having to predict, crystal-ball style, that it might happen. Without otherwise being able to wire itself into the operating system internals to give you a guaranteed warning. The Windows group at Microsoft hasn't ever been that happy about accommodating managed code, Longhorn was a sore spot for quite a while. Loader lock was a big, big issue in .NET 1.0
It almost certainly is a false warning in your case, you can be dead-sure that the CLR is already loaded, your program could not possibly start otherwise.
Fortunately it is very simple to make it stop bugging you: Debug + Exceptions, open the Managed Debugging Assistants node and untick the "LoaderLock" checkbox. Very high odds that it will leave you in peace from there, allowing you to focus on testing your program.