A valid JPEG file can be preview by just hitting the spacebar on it when highlighted in Finder. If that doesn't show you the image, then it isn't a valid JPEG image file..
Boy, we seem to have a few testy first time posters here today, maybe it's an Easter Good Friday thing!!
Anyway, Raz0rEdge the poster that you quoted is not mistaken. If you can or will accept that, then maybe some can help get your problem fixed.
You shouldn't be putting a Public Beta on a working partition anyway. Im afraid I think Apple got it wrong letting the public in on this, because there are so many people installing the Beta (so they have the latest and greatest and feel special) and then complain that it stuffed something up (not saying you did either).
Im a Developer, and ALWAYS have my Beta on a Separate Partition, so I can still do work, and also test.
Apple will put the 10.10.3 update out, when its good and ready and not before time. You really should have made a backup first, and then installed the Beta and use the backup to get to where you want to be, and not be waiting for the release.
Obviously you takes your chances with beta, which is why I have 3 backups...well 2 1/2 (long story). I also keep my data, including 5 virtual machines, on a separate drive from the OS, which is on an SSD (because SuperDrive is for suckas!). I'm not complaining about anything, nor am I particularly adverse to reinstalling, I'd just like to figure out what is causing Preview to fail, because my security badge says I'm an IT Specialist and I might see this again on a client's computer.
So far all I'm getting here is "Preview can't possibly fail!" – a bold and definitive statement that no tech professional would ever make about anything, and "You shouldn't use beta," which is just shorthand for "I have no idea how to address your issue". I shouldn't have even mentioned beta, it's like telling people in a general forum you're on a Mac...you'll get no response except "You should get Windows!" Clearly this is going to be another mac-forums login I'm going to completely forget about.
Again, not testy, just unimpressed.