Replace ASCII code force to use binary and show error message

I use this command to replace the ASCII character to another character:
C:\Fart.exe -cBVCb C:\temp\FartTest*.cms \x18 \x2A

Result as below:
C:\Temp>C:\Fart.exe -cBVCb C:\temp\FartTest*.cms \x18 \x2A
FART: --verbose
FART: --c-style
FART: --backup
FART: wild_card="C:\temp\FartTest*.cms"
FART: find_string="\x18"
FART: replace_string="\x2A"
FART: actual find_length=1
FART: actual replace_length=1
Warning: fart may corrupt binary files
FART: processing C:\temp\FartTest\,*.cms
C:\temp\FartTest\00001518.cms [12791]
Error: could not remove: C:\temp\FartTest\00001518.cms.bak
C:\temp\FartTest\00001519.cms [256]
Error: could not remove: C:\temp\FartTest\00001519.cms.bak
C:\temp\FartTest\00001520.cms [5142]
Error: could not remove: C:\temp\FartTest\00001520.cms.bak
C:\temp\FartTest\00001566.cms [38]
Error: could not remove: C:\temp\FartTest\00001566.cms.bak
Replaced 18227 occurence(s) in 4 file(s).

It keeps prompt "Error: could not remove:"

What can I do to make it work?

Best Regards,
Ivan