Mysterious item on my schedule

There is a box on my schedule that I can't select. I think it's a text box.

A mysterious item on the schedule. No clue what it is? Here are some things to look at:

Could it be a text box or a picture?

Go to Tools | Other Tools | Manage Symbols, Pictures, Freeform...
Pick Pictures and see if any pictures on the list are placed on a different page.

Could it be a floating legend?

On the Layout tab, click Full Legend. The toolbar switches to Current Object : Legend.
Floating Legend. If the mysterious object disappears and moves to the bottom of the schedule, then yes it was an empty floating legend.

Could it be a symbol with a text box?

If you are unable to click on a symbol, check out this article: Can not select symbols on some rows