Need help with hash_map

I am trying to use the following hash_map:

typedef stdext::hash_map< SYMBOL_KEY , poption_data > hm_greeksByOptionSymbol;

as defined by these types:

typedef struct _symbol_key
{
      // constructor
      _symbol_key( const char *pszSym )
      {
            if ( pszSym )
                  strncpy( szSym, pszSym, sizeof(szSym));
            else
                  szSym[0] = 0;
      }

      ~_symbol_key(){};

      // overload the less than operator
      bool operator < ( const _symbol_key key ) const
      {
            int iRet = strcmp( szSym, key.szSym );
            return (iRet < 0);
      }

      operator size_t() const
      {
            return hash_compare( szSym );
      }

      unsigned long  hash_compare(const char *str) const
      {
            unsigned long hash = 5381;
            int c;

            while (c = *str++)
            {
//                  hash = ((hash << 5) + hash) + c; /* hash * 33 + c */
                  hash = hash + c;
            }

            return hash;
      }

      char szSym[40];
} SYMBOL_KEY;

typedef struct _option_data
{
      _option_data() :
            bid(0),ask(0),delta(0),theta(0),gamma(0),vega(0),sBid(0),sAsk(0)
            {};

      long      bid;
      long      ask;
      long      delta;
      long      theta;
      long      gamma;
      long      vega;
      long      sBid;
      long      sAsk;
      long      impVol;
} option_data, *poption_data;


**********************************************************
upon calling the following line of code:

mcapi::hm_greeksByOptionSymbol::iterator iter = m_hmGreeks->find( sk );            // CAUSING ERROR *******


i get the error:

An unhandled exception of type 'System.AccessViolationException' occurred


NOTES:
The exception if occurring before the first entry is entered into the hash.  Any assistance would be appreciated.