Have you ever minimised AutoCAD (Windows 7 64) and not been able to maximise it from the taskbar? The button is live (glows when you hover), the preview shows the application and the full application window shows when you hover on the preview. Any attempt to maximise via the taskbar, or Alt+Tab, results in a “bong” sound and nothing.
Task Manager: The only way to get back
If you get stuck like this Ctrl+Shift+Escape to open the Task Manager then double click or Right Click > Restore will bring the application back.
AutoCAD, Windows or something beginning with VBA?
This behaviour only appeared when running a 3rd party app. It used a tiny, tiny, bit of VBA (which was installed) for a launch dialog but none once in operation. After that requirement was removed and the VBA component disabled the refusal to Maximise vanished.