PInvoke - .net 4 Vs 3.5 ?

I've an issue regarding p/invoke from managed to unmanaged code. See my original post at the MSDN forum (as brief summary is seen later in this post). Before I go on, I just want to explain a couple of things: I have a wrapper assembly in net 3.5 that does the actual interop to the unmanaged code. Then I have my console "host app" which uses the wrapper assembly. The solution I came up (I refer to my MSDN post) works when the host app is using .net 4, but it doesn't work when changing the host app to use .net 3.5. When changing, I get a AccessViolationException.

host app: 4.0, wrapper assembly: 3.5
-> works
host app: 3.5, wrapper assembly: 3.5 -> throws
AccessViolationException

Do anyone have a clue to why I get an AccessViolationException? Most importantly, how do I get it working with .net 3.5?

Brief summary on the MSDN post I refered to. I have this messy p/Invoke I need to solve. The C declaration looks like this:

long TBAPI TbeAndring (short,
short,
PTB_PU,
PTB_ANDRING_INFO,
PTB_PARAMS,

[CODE]...

Where PTB means that each argument is a struct pointer to an array of arbitrary length. The structs mostly contains strings, doubles, char and short. Anyway, I ended up with this DllImport statement:

<DllImport(NativeLibraryName, CallingConvention:=CallingConvention.StdCall, CharSet:=CharSet.Ansi, SetLastError:=True)>
Public Shared Function TbeAndring(ByVal sAntMoment As Short, _
ByVal sAntPU As Short, _

[CODE]...

As you see some of the arguments are changed by the unmanaged code as well.