■ The cursor is not on a program line that contains a valid
  expression. The Instant Watch command expects the cursor
  to be on an expression whose value you want to see.
 
■ Possible solution:
 
  • Reposition the cursor within the expression you want
    to watch and try again.
 
■ Tip: In a complex expression, it can be difficult to decide
       where to put the cursor. You can clearly indicate what
       the Instant Watch command should watch by highlighting
       it. Place the cursor to the extreme left or right of
       the expression and press Shift+right arrow or Shift+
       left arrow until the expression is highlighted.
 
■ If you need additional help, move the cursor to a keyword
  and press F1 to open the Help window.