Excel, Split screen, mouse not scrolling in active screen

Thank you Kidd_lp for your interest.

Unfortunately neither option has worked despite opening/closing/rebooting between steps to ensure any possible' baggage' was cleared.

I have however a new angle on this problem after further testing.

Ignoring your proposed adjustments, I have created a brand new Excel spreadsheet and tested this 'mouse scroll' issue. With a brand new spreadsheet, the mouse scroll problem does not exist and everything works as expected.

So the problem exists with documents created in a previous version. Not sure what I am talking about whether it is a previous version of Windows or Office.

I tried saving the document under a new name but that didn't work as expected but I tried it anyway.

Note: all my old documents are .xlsx documents, not the really old format although they may have come from .xls documents many years ago.

I have also opened a new document, highlighted the whole 9500 lined old document and copied it and pasted it into the new document. The new document with all 9500 lines is also now scrolling properly with the mouse upon opening however my forced page breaks never came across to the new document with Excel creating its own dotted line page breaks where it decides to put them.  I cannot accept losing my forced page breaks as each section is specific to my needs. 

I tried two copy techniques. One being highlighting all the columns and doing a copy / paste.

The second option was to click the blank cell on the left of the 'A' heading in the first column. This highlighted the whole document and I then did the copy/paste process.

Both options were successful with mouse scrolling but neither option brought across my specific page breaks.

So I either need Excel to save my current document without the old technology embedded in it or I need to copy the current Excel spreadsheet into a new document ensuring the forced page breaks appear in the new document.

At this stage I have to stick with the current document with my forced page breaks and continue with the mouse scrolling problem, unless you have a Plan B.

Once again, I thank you for your investigations to date.