You have to pass a reference to a NSError
object.. Parse will do the process and if any error is there it will update the error object with appropriate error.
You new code should be like
-(BOOL)registerUser{
NSError *error = nil;
PFUser *newUser = [PFUser user];
newUser.username = self.username;
newUser.password = self.password;
[newUser signUp:&error]; // error
if( error != nil)
{
//log the error or show alert
return NO;
}
return YES;
}