CDatabase link to CRecordset

[gidos]

im studying about Database with C++ support, i create a workspace for mfc dialog box,
name of workspace is ABC. the source files of C++ is on C:\VCDb. I create on ODBC the System DSN name ab, the driver of this is Microsoft Access Driver. On abc workspace i #include <afxdb.h> on StdAfx.h file, i create a button on abcDlg, i put this following codes:

void CAbcDlg::OnButton1() 
{
	// TODO: Add your control notification handler code here
	
	CDatabase A;

	A.Open( _T("ODBC;DSN=Ab"), FALSE, FALSE);
	
	MessageBox(A.GetDatabaseName()); 

	MessageBox(A.GetConnect()); 

	CRecordset B(&A);
		
	short nIn = 0;
	
	CString szSt;

	B.GetFieldValue( nIn, szSt); // got eeror here
	
	MessageBox(szSt);
	
	
}

When i press button1 MessageBox displays C:\VCDb\Dbfile, the second messagebox displays
ODBC;DSN=Ab;DBQ=C:\VCDb\DbFile.mdb;driverId=281;FIL=MSAccess;MaxBufferSize=2048;PageTimeout=5;
and an error dialog box displays debug assertion failed program: C:\VCDB\abc\Debug\abc.exe file: dbcore.cpp line: 1901.

please help me

thanks