请教个问题，C#调用c++ dll报了个异常：

An unhandled exception of type 'System.AccessViolationException' occurred in AlgorithmLib.exe

Additional information: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

C# code：

[DllImport(CSAlgorithmPath, EntryPoint = "?GetVersion@CSAlgorithm@algo@@QAEHPAD@Z", CallingConvention = CallingConvention.Cdecl, CharSet=CharSet.Auto, SetLastError=true)]
        public static extern int GetVersion(StringBuilder pVersion);

C++ code：

int CSAlgorithm:: GetVersion(char* pVersion)
{
boost::unique_lock<boost::recursive_mutex> lock(*m_mutex);
return m_algorithm->GetVersion(pVersion);
}

之前没有下划线的锁，没有问题，现在有锁了，请教应该怎么办？不能改C++的代码。

Thanks！