How to Insert/Remove Envelope - Volume

I have a new installation of Vegas Movie Studio 10 on a new PC. On my old PC I have Movie Studio 9 and do not have this problem. What is the problem? "Insert/Remove envelope - Volume" blue line does not appear, so I cannot use that function. I know how to use it, but the line simply doesn't appear, despite the function being enabled with a tick. Any clues? Peter C

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