Help sd card troubles

[714sithlord]

i just got a 32 gb sd card for my samsung vibrant. after i put it in i formated it threw the phone. then i movie a avi. file to it threw the phone. it moved and when i opened it it played fine but i tryed it a few minates later and it said " sorry that video can not be played . i moved it back to the phone memory and it corrupted the file. the movie file i mean. i tryed several times. reformating and moving ... the same thing everytime. the phone reads the sd card and shows that i have 31 gb and change left on it. help me obi-won your my only hope. what am i doing wrong?