I answered it here :
One thing I missed from the description is I turned off the maximize button. When I tried to enable this property again, the taskbar reappeared. Apparently, it assumes that if you do not want the maximize button, you are creating a kiosk-style application in which you do not want your users to see anything other than the application screen. Not quite what I expect, but it works, I think.
I had this problem and it was solved with the help of Jeff. First, set windowstate to Maximized. but do not disable MaximizeBox. Then, if you want MaximizeBox to be disabled, you must do this programmatically:
private void frmMain_Load(object sender, EventArgs e) { this.MaximizeBox = false; }
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