glibc detected double free or corruption

[Fabio.DAndria]

Dear all,
        I have the following problem: I made a class (CDatabase) with some 
simple methods. The one I use to return the queries results is the 
following:

Result CDatabase::ReturnQuery(string query)
{
        try
        {
                //executes a query and returns a resultset back
                Query myQuery = myConn.query();
                myQuery.reset();
                //sets the query text
                myQuery << query;
                //executes the query
                Result myResult = myQuery.store();
                return myResult;
        }
        catch (BadQuery er)
        {
            cout << "DB error: " << er.error << endl;
                return NULL;
        }
}

In the main class of the program I have a  call to the global CDatabase 
object (myDB) as the following:

 bool CCheckThread::Check()
 {
        //check if there is a new record on the DB
        Result myResult;

        myResult = myDB.ReturnQuery("select id from task where status_id = 
0;");

        if(myResult.size()>0)
        {
                Result::iterator myCounter;
                Row myRow;

                //for every record found we launch a CSessionThread which 
is going to handle it
                for 
(myCounter=myResult.begin();myCounter!=myResult.end();myCounter++)
                {
                        if(!myShutdown)
                        {
                                //logs that the new session was found
                                pthread_mutex_lock(&myLogMutex);
                                myLog.WriteLog("I", "A new session was 
found. Starting analysis");
                                pthread_mutex_unlock(&myLogMutex);

                                myRow = *myCounter;
                                long myId = (long) myRow[0];

                                if(pthread_create(&myTaskThread_t, NULL, 
&StartTaskThread, &myId)==0)
                                {
                                        myThreadNumber++;
                                        //sleeps 2 seconds in order to let 
the thread start
                                        sleep(2);
                                }
                                else
                                {
                                        pthread_mutex_lock(&myLogMutex);
                                        myLog.WriteLog("E", "Could not 
create CSessionThread");
                                        pthread_mutex_unlock(&myLogMutex);
                                }
                        }
                }
                return true;
        }
        else
                return false;
}

The problem is that whenever I have no records found, when the function 
ends I have a segmentation fault with the following message "*** glibc 
detected *** double free or corruption: ". If records are found no 
problems. I am wondering where the problem could be, even debbuged via 
xxgdb.

I checked for the previuos messages but haven't found anything about this. 
Could you please help me out ?

Regards
Fabio