I have a guitar with superlight ernie ball electric strings. And every time I tune one string, the previous one goes out of tune. Anyone know what that could be?
Don't do it man. You take one inhaling of marijuana and the next thing you know you're standing infront of a murdered prostitute with a bloody knife in your hand.

At least, that's what the anti-drugs people at my school tells us.
I'm assuming your playing a standard acoustic guitar with a fixed bridge.

1) Personally I wouldn't use electric strings as they are already super thin and I hate how they sound on acoustic but if you like it whatever.

2)If your your strings can't hold a tuning it probably because your tuning heads are slipping, they can usually be tightened. Even if you do need new ones it won't cost you more then $80 bucks for a nice set.

3) It's entirely possible you messed up when you where re-stringing your guitar or was to lazy to do a proper job, I ended up doing this once and ruined a set of strings because one snapped. So if there is nothing wrong with your Tuning knobs then it's probably just because your strings are slipping.