user32.dll error in Safari 4

I installed Safari 4 about a week ago. (previous Firefox user)

everytime i click onthe Safari icon, either on the desktop,
or in the quicklaunch toolbar, i get this window:

*"safari.exe entry point not found"*
"The procedure entry point IsThreadDesktopComposited could not be located in the dynamic link library USER32.dll."

I click okay to get out of that window, and then Safari opens as usual.
Works okay. But I don't know what those error messages are about.
I've uninstalled and re-installed Safari 4 twice, but problem persists.

Anyone know why this is happening? And how to correct this?

thanks!