Hallo
I have only one copy of Microsoft messenger on my PC. I was online with someone and I had two icons showing in the taskbar. One showed I was online and the other showed I was not. This made it look as if I had two different accounts. This question may seem trivial but it is important to me to get an answer.
Regards

It doesn't matter how many copies you have on your PC.
What matters is how many times Messenger was started up
(and if you have enabled 'polygamy' in Messenger Plus! or via any other addon or via the special registry setting MultipleInstances).

Check the Task Manager (press CTRL+ALT+DEL) to see if you have multiple processes called msnmsgr.exe running. If so, then you have your answer; for each Messenger session there will be an icon in the traybar.

If there is only 1 process msnmsgr.exe process running, and you still have more than one icon, then try to hoover over the icons with your mouse cursor and see if they dissapear. If they do, then the other icons are leftovers of a crashed Messenger.

If you have enabled 'polygamy' then a new Messenger will start each time you double click on the Messenger shortcut or each time Windows launches Messenger (eg: via your startup entries in Windows).

Polygamy can be enabled/disabled:
- via Messenger Plus! via the menu Plus! > Preferences & Options > Features > Multiple Accounts > Allow me to connect to several accounts simultaneously
- Or via patching Messenger by the use of patchers like A-Patch.
- Or by setting the registry value HKLM\SOFTWARE\Microsoft\Windows Live\Messenger\MultipleInstances