Passing a string from C# to Matlab

I'm calling a Matlab mcc-compiled DLL from C# and am attempting to marshall a string as an input parameter. I am using .Net PInvoke to load and call the DLL and have declared the method as follows:

public static extern void func([In]Int32 nargout, ref IntPtr h, [In][MarshalAs(UnmanagedType.LPStr)]string path);

and the call as:

string dataPath = "c:\\path\\data";
int nargout = 1;
IntPtr h = IntPtr.Zero;
func(nargout, ref h, dataPath);

This results in an exception "Attempt to read or write protected memory".

I have also tried passing a char array:

char[] tmpStr = dataPath.ToCharArray();
func(nargout, ref h, tmpStr);

And have tried using the runtime mxCreateString function: [DllImport("mclmcrrt72.dll", EntryPoint = "mxCreateString", CharSet = CharSet.Ansi)] static extern IntPtr CreateString([In][MarshalAs(UnmanagedType.LPArray)] char[] myString);

with call:

IntPtr strPtr = CreateString(myStr);
func(nargout, ref h, tmpStr);

However, the same exception is encountered.

Without the string parameter, the call succeeds.

Has anyone succeeded in doing this?

Thanks in advance.