'System.AccessViolationException' in Oracle.DataAccess.dll

public System.Data.DataTable GetTableMd5(AbsDataReader _reader) {

System.Data.DataTable =_table System.Data.DataTable();

            if (_reader == null) {
                return new System.Data.DataTable();
            }
            Hashtable lstFormats = new Hashtable();

            _table = _reader.GetSchemaTable();

return _table;

}

when calling the GetSchemaTable() method getting the below error
Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
Can you please help on this how can i solve this??
thanks in advance