Error while updating manager in Windows 10
Make sure that all your windows updates are installed and reboot your computer. This problem is not a manager issue but rather that you have updates or something that is pending a reboot. Install your windows updates and restart - then you can install Manager. I had the same thing happen to me when I was installing a program (not manager) on windows 10 and it turned out that there windows updates wanting to be installed.
done as all you said. Still same error. 
It seems from a google search that this is a common problem with Windows 10.
Here is a page reporting similar issues installing different software Another Installation is already in Progress
What you can do “go into task manager there is a process called windows installer. msiexec.exe appears to be included in this. I 'end task’ed it and that solved the problem.”
From reading on the Internet my opinion is that its windows update causing the problem. Go back into windows update and ensure that there are no more updates waiting to be installed because sometimes windows does not install all updates in one go - it can require several reboots.
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THIS WORK AROUND WORKED FOR ME TOO !!! 
THANKS A LOT.
Brilliant. 
Glad I was able to help.
When you stopped the installation service did it tell you what program was trying to finish installing?