求高手解决c#平台调用的数据封送问题

现在我需要在c#中调用一个外部dll文件的函数。代码如下：

c++的dll文件中的原函数：
typedef void (__stdcall *fp_SETUPdllTYPE)(long &,char*,char*,char*,long &,char*,long ,long ,long ,long );

我在c#中的调用代码:
[DllImport("refprop.dll")]
private extern static IntPtr SETUPdll(ref int l1, StringBuilder s2,
StringBuilder s3, StringBuilder s4, ref int l5, StringBuilder s6, int l7,
int l8, int l9, int l10);

int i=1, ierr=5;

StringBuilder hf = new StringBuilder("nitrogen.fld");
StringBuilder hrf = new StringBuilder("DEF");
StringBuilder herr = new StringBuilder("NO");
StringBuilder hfmix = new StringBuilder("hmx.bnc");

SETUPdll(ref i, hf, hfmix, hrf, ref ierr, herr, 20000, 255, 3, 255);

目前无法运行，不知道什么问题，请高手指点，小弟跪求