This is due to corruption of the SB.MSG file where stored with user ID & the corresponding password.No one can make use of a corrupted file, and therefore retrieve from previous
version will be neccessary. Usually, SB make a backup zip file during backup and this file
is named as SB.ZIP in the same sub-directory of SB.
First rename the corrupted file to another name,
  i.e. REN SB.MSG SBO.MSG
Then Locate the file first by typing dir SB.ZIP <Enter>
If the file is there, user pkunzip to get the SB.MSG file out.
PKUNZIP SB.ZIP SB.MSG <--- the system will take the last copy of
SB.MSG from the zipped file SB.ZIP.
test the sb program again to confirm everything is normal.