Displaying popup

I have a script in which I want to display a popup, then call a web service to perform an action. It appears that the popup is not actually displaying until the web method call completes. Is there some method I can call to have the system display the popup before making the web method call?

Can I see your script?

This is within a button actionPerformed script:

    system.nav.openWindow("Popups/PrintingLabelsPopup")
system.nav.centerWindow("Popups/PrintingLabelsPopup")

wsdl = "http://server/transservice/transactionService.asmx?WSDL"
client = suds.client.Client(wsdl)
res = client.service.PrintLabel( woNum, qty, cntOp )

If I disable the last 2 lines, the window opens immediately.

Figured it out. Used the invokeAsynchronous method to call the web service asynchronously.