Name Manager Won't Open

[aerdef]

I have seen the before, but could never fix. Suddenly in a file, I cannot invoke the Name Manager window either by button or keystroke (I still use the old Alt I+N+D). I type pretty quickly so maybe I hit some "toggle" that I don't know about? Everything else in name manager works (I can create one, etc). This is book specific. If I open an another file, it works. Again, just randomly in random workbooks.

thanks