Just a stab in the dark, are you reading the tapes with the same
blocksize as they were written?  This bit me recently.

Steve
-- 
Steven J. Backus                        Computer Specialist
University of Utah                      E-Mail:  steven.backus AT utah DOT edu
Genetic Epidemiology                    Alternate:  backus AT math.utah DOT edu
391 Chipeta Way -- Suite D              Office:  801.587.9308
Salt Lake City, UT 84108-1266           http://www.math.utah.edu/~backus