If you use Pidgin, a popular all-in-one IM client, and you use the Guifications plugin then you might have this problem. You have a buddy in more than one group and Guifications notifies you twice (or more) for that same buddy. Here is a fix to that:
Right click on one of the buddys in your list.
Select “Guifications Theme”
Select “None” and click OK
This sets to to have no theme (or to basically not show the popup) for that contact. You can also do this to an entire group as well. This is useful if you have the “Mobile Device” group (which is there if you sign on to AIM on a mobile phone)
Hoped this helped anyone. Please leave a comment and sign up at the forum 🙂