Can't get window class to work

I'm at a complete loss. I can't get window class to work, at all. Example:

WinActivate("[CLASS:Notepad]")

Doesn't bring notepad window forward. Whichever scripts I've ever written, window class name never worked for me. AutoIT 3.3.8.1; Windows 7. I think I even had the same issue in WinXP.

What can be the problem?

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Hmm... I don't know... works half of the time. Maybe Im just making errors in scripts. I better withdraw my question until I have more details. It could be my mistake. Pardon me for the inconvenience.