Macro inexplicably stops after Workbooks.Open

[thinkfiat]

I am a novice at excel macro programming.

My Excel 2000 macro inexplicably stops after the line:

Workbooks.Open Filename:=stAddrFullname, ReadOnly:=True

1) I know that the remainder of the code is not executed because a breakpoint on the following line is never reached.
2) I know that this line is executed because the stAddrFullname workbook is clearly opened and is displayed when the code stops prematurely.
3) No error message is displayed and I have no 'OnError' instructions in the code.
4) (This is the bit I really don't understand). If I put a Breakpoint in the macro anywhere in the function preceding the "Workbooks.Open" statement, the macro reaches the Breakpoint and then runs through to completion with no problem. When I remove the breakpoint, it reverts to stopping as soon as it has opened the Workbook.
5) The stAddrFullname workbook has no macros in it.

Any ideas please? It is very hard to debug something when the debugging seems to change the sequence of events.

[royUK]

What is the rest of the code?

[Reafidy]

Cross Posted here

[thinkfiat]

Apologies for unattributed cross-post on Ozgrid.

I stripped the code down to the few lines shown below and it is now apparent that the problem is down to how I initiate the code.
1) From a button it executes ok.
2) From Macro Shortcut CTRL+J it works ok.
3) From Macro Shortcut CTRL+SHIFT+J it stops after "Workbooks.Open"

What is special about CTRL+SHIFT+J and why does it specifically stop after the Open command?

Sub UpdateDB()

Dim stAddrName As String
Dim stTemplateName As String
    stTemplateName = ActiveWorkbook.Name
    stAddrName = "C:\Mobile Order Addresses.xls"   'Actually a clear worksheet
    Workbooks.Open Filename:=stAddrName, ReadOnly:=True
    Windows(stTemplateName).Activate
    Range("A1") = "FINISHED"
End Sub