Application error after closing

[Metalpalo]

Hello

I have got one VB6 application working on ORACLE database via DAO. In case that application runs longer time and I close it then I got following error:

The instruction at "0x7c921689" referenced memory at "0xffffffff". The memory could
not be "read".

Click on OK to terminate the program.

This problem doesn't occurr on all computers. It seems that problem can be in connection with database.

Or where can be this problem. How can I determine failure?

Thanks

[Metalpalo]

Hello

One note:
Old version of application doesn't handle closing of connection to database.
Therefore I added this source code into Unload method:

Err.Clear
On Error GoTo ErrorHandler
    MyDataBase.Close
    Set MyDataBase = Nothing
    MyWorkSpace.Close
    Set MyWorkSpace = Nothing
    Exit Sub
ErrorHandler:
    MsgBox Err.Description, vbOKOnly + vbCritical

Old versions without this handling work fine.
Can it cause this problem?

I note again that application exits with this error only in case of longer running e.g. half a day and only on some mashines.

Thanks

[HanneSThEGreaT]

OK, don't shoot me for my comments. But why are your connections open for such a long time ¿ Isn't there any way you could perhaps only open the DB once needed, and close it after all your processing is done ¿

[Metalpalo]

This way you preferre is not suitable because most of application's operations work with database and connecting/disconnecting every time takes some time and would slow the application.

Any ideas?

[Optional]

Opening a connection and using it to call a stored procedure or execute a piece of SQL and then close it does not take extra time.

What takes extra time is when your application has to deal with multiple open connections which never get closed. That's one sure way to introduce a memory leak. Memory leaks slow down applications, potentially freeze it and generate all sorts of memory errors.

For example, you would always have 1 generic method GetConnection and another DestroyConnection (or what ever you want to name them).

You return a connection object from one and pass it to the other for destruction. you call those generics everytime you want to execute anything against the database.

You are most likely getting the error due to references in memory to an object (propably a connection object) still having a handle to the application when you are closing it.

Not opening and closing a connection after you are done using it everytime is very bad practice.

Off course, this does not mean there never is a reason for having a constant open connection in any application, just your reason is not it.

Edit
You could also get the error if you are trying to close the connection during unload after internal VB code has already partially disposed of the object.
Again, try opening and closing the connection everytime you use it.
Either that or undo your code changes. It's the only 2 options I can see how to debug this issue.