Same thing here. Will have to work with ver. 7.4 until you guys figure out what the issue is. Please let me know how to resolve.
This update installation process is completely different from previous ones where updates would install within Muse application; this update takes you to Adobe application website - offers "Download" of Muse 2014. This is confusing to me...does this mean download a completely new Muse or install an update? Clicking download offers me all CC applications "Try, try, try" etc. or, for Muse to "Install". Clicking install eventually brought me to OP's issue above.
Please help...