When you come across "Invalid Pointer" error in Transform data task under DTS package then one possibility is because the source sql statement returns NULL warning message.
Try to run the source sql statement in query analyzer and it should be returning NULL warning at the end of the result. This might be because we have missed handling the NULL data. We might have used aggregate function in the query and if the data for that field has null data then we would get this warning message.
To handle this we might have to handle the null data using coalesce or avoid null data.
HTH.