Probably the images were moved to a system where the CPU byte order is reversed from the system on which you created the files. Many ANALYZE format reading programs do not recognize this possibility (AFNI does) and so will be very unhappy with the images.
The solution would be to have a program that properly byteswaps the .hdr and/or .img files. But I don't have such a program in my repertoire, since AFNI doesn't need it. Any volunteers?
bob cox