Hallo,
when I tried to install Mathcad 11 on a new Computer with Windows 8.1, everything went wrong, no chance. On my old notebook with Windows 7 the program worked correctly.
Some days ago i upgraded the notebook from Win7 to Win10. And I had very much luck : mathcad 11 still works.
Then I upgraded the computer from Win8.1 to Win10 an tried to install mathcad 11. The installation went complete through, but then allways came the message "incompatible programm". Also some tries with compatible modus from win95 to win7 did not help.
I use mathcad 11 from now on on the old notebook. Better then nothing or the unloved Mathcad Prime.
The solution with the "MSXML 4.0 SP2 Parser and SDK" is too risky for me.
From Germany, Gerd-Wilhelm