Cannot evaluate expression because a native frame is on top of the call stack- getting error

Hi All,
I am developing a windows application which using VS 2010, in this application I am using firebird 2.5 database and c#.net language.
 
when i am debugging my application I am getting an error message, showing "Cannot evaluate expression because a native frame is on top of the call stack" I am getting this message at the step 3.

1. if (IsAlreadyRunning())
2. {
3. SwitchToCurrentInstance();
4. return false;
5. }</pre>
6. Application.Run(frmMain);
in my singleinstanceApplication class and also at the while statement for reading the data from the DataReader object.

FbDataReader reader;
                       cmd.CommandText = "select acct_name from iaccounts where comp_id=" + GlobleData.Companyid +" Order By (acct_name) asc";
                       reader = cmd.ExecuteReader();
                       if (reader.HasRows == true)
                       {
                           while (reader.Read())
                               autoCompleteStringColl.Add(reader["Acct_Name"].ToString());
                       }

 

What are the reason for this type of errors? Can any one solve my doubts Please.