Are you using a Tablet PC, by any chance?
Here are some recent Google Groups threads about similar issues.
http://tinyurl.com/9mvop
http://tinyurl.com/7md5w
http://tinyurl.com/djheg
Generally, this happens when some utility intercepts your copy/paste
actions. It can also be caused by inadvertently hitting your Fn key on your
laptop, a faulty keyboard, etc.
You might need to figure out when "sometimes" is.
Does the machine print screen when you right-click to copy/paste, when you
use Ctrl+C and Ctrl+V, and also when you click the copy/paste icons on the
toolbar?

Signature
Echo [MS PPT MVP]
http://www.echosvoice.com
Fixing PowerPoint Annoyances
http://www.oreilly.com/catalog/powerpointannoy/
> Hi All,
>
[quoted text clipped - 13 lines]
> Thanks
> Alan
AF - 16 Feb 2006 01:39 GMT
Hi Echo,
No, I am using DELL OptiPlex GX 280 Desktop computer and the keyword is
Microsoft wireless keyboard.
Let me try to work out the "print screen" is triggered by Ctrl+C and V or
copy/paste action or right click. (But the problem will just occur 1 or 2
times of 10 copy and paste actions)
Thanks
> Are you using a Tablet PC, by any chance?
>
[quoted text clipped - 31 lines]
>> Thanks
>> Alan