The simple fix I did to finally get it to work on Steam was going into my C:\Program Files (x86)\Steam\steamapps\common\Steamworks Shared\_CommonRedist\vcredist\2015 and deleted the file called installscript.vdf. Game started right up.
On a side note, I was able to bypass the error and play by running the BardsTale4 application file in The Bard's Tale IV folder: C:\Program Files (x86)\Steam\steamapps\common\The Bard's Tale IV but it was not running through Steam so I am guessing you wouldnt get any badges or whatever. But it was a way to play if you absolutely need to play!
