Went to run DCS and Steam wants me to install the sim again. I just ran it a week ago and Steam seems to have my hours played correct and my last run date, but it now wants me to install the sim like I have never played it.

What is the deal?

My files are still on my hard drive and I do not want to reinstall the game since it is HUGE. Let alone re configuring everything.
Before I go fooling with it, any help is greatly appreciated.