Error upgrading MSSQL 6.5

On installing Service Pack 5a on MS SQL Server 6,5 I receive an error
"Setup initialization could not be successfully completed.
  cfgchar.exe could not be executed. Please check the relevant
  out file".
This error is documented in Redme.txt file of the Service Pack and it says
that the reason is quotation marks in the variable PATH, but even with
corrections in the PATH I still receive the same error.
Any idea?