PRB: Debugging ActiveX Server in IDE Causes Application Error

• Microsoft Visual Basic Professional and Enterprise Editions for Windows, version 5.0 on the following platform: NT

SYMPTOMS

When debugging an ActiveX server running in the Visual Basic IDE on Windows NT 4.0, you may receive the following error when the ActiveX server attempts to return control back to the Client application running in a second Visual Basic IDE:

   "Step Into: VB5.EXE - Application Error
   The instruction at <memory address> referenced memory at <memory
   address>. The memory could not be "read"

RESOLUTION

To correct this problem, use one of the following methods.

• Install Windows NT Service Pack 2 or later. The system requirements on the Visual Basic Box recommend Service Pack 2 for Windows NT 4.0.

  -or-

• Use late binding when creating the ActiveX server object.

MORE INFORMATION

A common method of debugging ActiveX servers is to run them in one session of the Visual Basic IDE while the client runs in a second session of the Visual Basic IDE. When using early binding to an ActiveX server on Windows NT 4.0, you will receive an APPLICATION ERROR when the ActiveX server tries to return control to the client application.

NOTE: This is a problem only if Windows NT Service Pack 2 or later is not installed.

Steps to Reproduce Behavior

1. Create a new ActiveX EXE Project.

2. Name the Class "clsTest" (without the quotes).

3. Add the following code to the class module:

         Private Sub Class_Initialize()
            Debug.Print "Class Init"
         End Sub
   
   

4. Click Properties on the Project menu. On the General tab, set the Project name to "pjxTest." On the Make tab, set the Application Title to "pjxTest." On the Component Tab, set the Start Mode to ActiveX Component and click OK.

5. Run the ActiveX server by pressing CTRL+F5 or, from the Run Menu, select Start with Full Compile.

6. Start a second session of Visual Basic and create a Standard EXE project.

7. From the Project Menu, select References. Check "pjxTest" and click OK.

8. Place a CommandButton on Form1.

9. Add the following code to the form:

         Dim obj As pjxTest.clstest
   

         Private Sub Command1_Click()
            Set obj = New pjxTest.clstest
         End Sub
   
   

10. From the View Menu, select Toolbars, and make sure the Debug Toolbar

        is checked.
    

11. Use the Step Into button on the Debug Toolbar to step through the code.

        You will get an APPLICATION ERROR when you click the Step Into button
        and you are on the "End Sub" line in the Class_Initialize Sub of the
        ActiveX server. Because the APPLICATION ERROR is from the Client,
        the Client session of Visual Basic will be terminated.