What is it you want to view side-by-side? I ask that because, if it is gray
out, that means you only have one Excel file loaded... you need two loaded
in order to view them side by side. If you want to view two different parts
of the same Excel file, you can use the Split functionality. Either click
the Split button (to the left of the View Side by Side button) to create a
4-panel view of your file (you can drag a splitter "off the sheet" to reduce
the view to two panels) or grab the little button looking rectangle above
the vertical scroll bar's top arrow or the button looking rectangle to the
right of the horizontal scroll bar's right arrow and drag them into the
inside area of the sheet.

Rick