Okay so a while back, about the time Angry Birds demo came out, my phone started giving me a message when installing apps saying "installation failed unknown reason-18" so for a while I just lived with it until finally I just wanted it fixed. So at first Sprint just told me to do a hard reset, then they did a reset that only they can do that is supposed to be better, the problem was still there, so eventually they said they would just get me a replacement phone. I just got the phone today and when I went to install stuff it gave me the same error code. I thought about the only things that have stayed consistent between the phones and the only things are the battery, SD card, and my gmail account. I figured the battery wouldn't do that so I decided to unmount the SD card and try and it installed perfectly so I figure I need to reformat the SD card but I don't exactly know how to do that so I came here to ask and also see if anyone knows if there is a certain file on the SD card that would cause that. Please help because I don't want to have to unmount the SD card every time I try to install something. Also I am a Mac user incase that changes anything. Oh and I wasn't sure exactly were this should go so if I posted this in the wrong area could a mod please move it.