Some times When you check your TasKbar properties or when you hide or unhide icons you can see old icons from Uninstalled or old programs yuo dont have anymore.

This Tweak will help you how to get rid of this problem Thanks to leobull of Xperience.org

How To clear the Past Items or Icons list in the TaskBar, perform the following steps:
1.Open Regedit Navigate to:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\TrayNotify

2.Delete the IconStreams and PastIconsStream values

3.Open Task Manager, click the Processes tab, click Explorer.exe , and then click End Process .

4.In Task Manager, click File , click New Task , type explorer , and then click OK .