Excel dialog is not being displayed

Hi,

Hopefully someone can help me with this. But first, an explanation.

I used Excel 2003 to make an add-in (which allows me to connect to a web service).
Opening a new sheet and using the menu, I can connect to the service. The menu simply runs a sub (ie: "connect_to_ws") which shows an excel dialog which prompts me to enter the WSDL file, name & password.
so far so good. I can then use functions to retrieve data and save my new excel sheet.

When I re-load my excel sheet, excel will try to recalculate the functions.
A function will check to see if there is a connection to the web service.
If not, it will run the same sub (ie: "connect_to_ws") which is called from the menu.
Only this time the dialog is simply not shown. And no error is displayed.

Can anyone help me with this? It seems that when Excel is busy recalculating, no dialog can be displayed. But yet the command msgbox will show messages.

NOTE: I use "If (ThisWorkbook.DialogSheets("webservice").Show = True) Then" to display the dialog.

Thanks
JPC

Your information is too scarce for me to analyse possible causes.
You'd better post the whole code.