2.2 back to 2.1

[Guest buff69]

please help i know there are post's on here but i dont understand i have 2.2 on my streak but have to go back to 2.1 so i can use a rebel sim card i have down loaded the 2.1 and renamed it put it on my sd card but it keeps coming up with an error code 2 what am i doing wrong please help to keep my sanity thanks