The error almost certainly relates to not finding CMD.EXE

Consider wrapping %COMSPEC% in quotes to preserve the path.

Also, when executing KiXtart in a new environment it's usually a good idea to fix the current working directory:

 Code:
BREAK on
; Fix current working directory
GO C:
CD \
If Exist("C:\test.bat")
 "C:\test.bat found"+@CRLF
Else 
 "C:\Test.bat not found"+@CRLF
EndIf

; Wrap %COMSPEC% in quotes to preserve the path - especially useful if it contains spaces.
Run '"'+%COMSPEC%+'" c:\test.bat'
"DEBUG: " + @ERROR + " - " + @SERROR+@CRLF
get $x