how to take snapshots in special cases

[Abhishek Dixit]

I have been taking screen shots on ubuntu via the PrintScreen key
which still is working.However if I click the network icon in top
right hand corner and want to take screen shot of this (with network
icon such as available wireless networks in drop down menu) then the
print screen key does not work .Same is the case with volume or
battery or bluetooth icon in panel.If I click on volume icon and there
appears a vertical bar to increase or decrease there I pause for a
moment I can not take screen shot at that moment.How ever if I again
click the volume icon in tray and the vertical bar disappears then I
can take the screen shots.So in this situation if I want to take
screen shots of the icons then what can I do?
As an example my print screen key will not take a screen shot of following kind
http://www.dedoimedo.com/images/computers/ubuntu-8.10-tp-wireless-1.jpg

Where as I can take a snapshot of this
kindhttp://www.dedoimedo.com/images/computers/ubuntu-8.10-shutdown-2.jpg

Note in the first link the person was able to take the screen shot of
wireless drop down menu which I can not take with my print screen key.

-- 
Regards
Abhi