C#尝试读取或写入受保护的内存。这通常指示其他内存已损坏。调用C++dll的方法出的错

[史_老师]

在网上查的是说我的数据类型错误，但是我不知道是哪里错了？求大神解救！！
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错误代码行：emReturnType = eshong_ipcsdk_invoke.IPCClient_Logon(logoninfo,ref hClient);
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IPCClient_Logon方法：

[DllImport("IPCSDK.dll", EntryPoint = "IPCClient_Logon", CallingConvention = CallingConvention.Cdecl)]
public static extern emReturnType IPCClient_Logon(LOGON_INFO pLogonInfo, ref IntPtr hClient);
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LOGON_INFO 结构体：

public const int name_len = 32;
public const int pw_len = 16;
public const int emLen_IP = 10;
public const int emLen_Name = 10;
public const int emLen_Password = 10;
public struct LOGON_INFO
{
[MarshalAsAttribute(UnmanagedType.ByValTStr, SizeConst = emLen_IP)]

// szDeviceIP：设备IP
public string szDeviceIP;
[MarshalAsAttribute(UnmanagedType.ByValTStr, SizeConst = emLen_Name)]
//szDeviceName：设备的名称
public string szDeviceName;
//nDevicePort：设备的端口
public Int16 nDevicePort;
[MarshalAsAttribute(UnmanagedType.ByValTStr, SizeConst = emLen_Name)]
//szUserName：登录设备的用户名
public string szUserName;

[MarshalAsAttribute(UnmanagedType.ByValTStr, SizeConst = emLen_Password)]
//szPassword：登录设备的密码
public string szPassword;

// pContext：上下文
public IntPtr pContext;

//bRegHeartbeat: 是否注册心跳，如果是公网的的设备，就不要注册心跳，默认为TRUE
public Boolean bRegHeartbeat;

//dwTimeout：登录超时时间（毫秒）
public int dwTimeout;
}这是引用的C的结构体
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c原来的结构体
typedef struct tagLOGON_INFO
{
char szDeviceIP[emLen_IP];
char szDeviceName[emLen_Name];
int nDevicePort;
char szUserName[emLen_Name];
char szPassword[emLen_Password];
void *pContext;
BOOL bRegHeartbeat;
DWORD dwTimeout;
tagLOGON_INFO()
{
ZeroMemory(this, sizeof(tagLOGON_INFO));
bRegHeartbeat = TRUE;
}
}LOGON_INFO, *LPLOGON_INFO;
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