I had the same problem a little while ago and got this message from Rob Bovey:

With Excel shut down, search your hard disk(s) for a file called
Excel.box (it's the VBE toolbox equivalent of an Excel .xlb file). Delete it
and then restart Excel. That may do the trick.

And this message from Tom Ogilvy:

It appears to be just a special multipage control.

If you right click above the tabs, you get a shortcut menu that allows you
to add and delete pages.

If you right click on one of the tabs, you get the additional controls popup
menu. Select that and just click the controls you want on the tab/page.

I believe I did a little of Tom's suggestion, until I broke down and just did
them all at once with Rob's suggestion.

(It scared the heck out of me!)

Nazerv70 wrote:

I've been developing an Excel App with about 4 User Forms. Recently, all the
controls in my Toolbox, except for "Select Objects", have dissappeared. When
I right-click and select "Additional Controls...", sure enough everything is
unchecked. So, I go ahead and re-add the "Microsoft Forms 2.0..." controls
and they show up again in my toolbox. However, if I exit the VBE and Excel
and go back in, once again my Toolbox is empty. What's going on??

--

Dave Peterson