converting float values

Question

I get data through a stores procedure from MS SQL db.

the values are,

int ID,

string name,

float distance..

i wrote this code in my c#   DBAccess class.

  rdr = com.ExecuteReader();

                while (rdr.Read())

                {

                    Merchant merchant = new Merchant();

                    merchant.ID = rdr.GetInt32(0);

                    merchant.name= rdr.GetString(1);

                    merchant.distance= rdr.GetFloat(2);

                    lstMerchant.Add(merchant);                   

                } 

but it gives me an exception  "Specified cast is not valid."

This is given by   "merchant.distance= rdr.GetFloat(2);" line...

What can i do??

please help me..Thank you.