Recovered files are red and won't open

My Toshiba external hard drive broke and a friend used a program on his mac to recover the files. He says it worked but now all the files are highlighted red and won't open. The file sizes look right, but for instance when I try to open a .mov file it says, this is not a movie file. Does anybody know what the problem is and what I need to do to get the files usable again? It looks like someone had this exact problem in 2010: https://discussions.apple.com/message/12408596#12408596
but I haven't been able to find an answer.