I've heard of this error from a couple of people so far and I haven't yet figured out exactly what change in Sierra is causing it.

The error comes from Wineskin needing to change the Info.plist file. When it tried to open the file for writing access the OS gave an "access denied" error.

To find the file right click the MoI app and choose "Show package contents" then inside there go to Contents and you'll find the Info.plist file, right click that and choose "Get info" and in the info pane go down to the bottom section named "Sharing & Permissions", if you expand that section does it say you have both read and write access to the file or does it say something like read only? Maybe you will need to take ownership of this file in order for it to be modified, I don't know why that's different since Sierra though.

Also does it get fixed if you just move the app into the /Applications folder like Martin mentions above?

- Michael