Ken,
What does the backup server log say?
%SYBASE%\ASE-15_0\install (Default)
Sounds as if the port is already in use.
Does it start if you change the port number in sql.ini?
Also see this:
After change BS entry in SQL.INI from hostname and NLWNSCK protocol to IP address and TCP protocol the issue was solved.
[RH2008VM_BS]
master=TCP,10.168.26.49,5001
query=TCP,10.168.26.49,5001
Regards,
Ryan