Using DLLs written with C++ with .Net applications

I recently had to reference a DLL in my C# application using Visual Studio 2010. It appears it was written in C++ and I ahve to check "use unsafe" It uses a simple method. The code is below. It runs fine on my 32 bit system but I get the error below when I run it on my 64 bit system. I tried everything in the configuration but it will not run. Any suggestings would be appreciated

static void Main(string[] args)
       {
           string file = "STGFEWR"

           var reesult = Calculate_Retention_Time(file);
       }
       public static double Calculate_Retention_Time(string sequence)
       {
           unsafe
           {
               SSRCalc.Class1 c = new SSRCalc.Class1();
               char* p = (char*)System.Runtime.InteropServices.Marshal.StringToHGlobalAnsi(sequence).ToPointer();
               double hydrophobicity_factor = c.TSUM3((sbyte*)p);
               return hydrophobicity_factor;
           }
       }

Could not load file or assembly 'SSRCalc.dll' or one of its dependencies. The application has failed to start because its side-by-side configuration is incorrect. Please see the application event log or use the command-line sxstrace.exe tool for more detail. (Exception from HRESULT: 0x800736B1)

Tags: C++, C#