I presume you are not using the latest KiX version?
Code:

If NOT @LOGONMODE
	Break On
EndIf
If Exist("\\@WKSTA\C$\")
	? "Yeah"
Else
	? "No"
EndIf
? "Error " + @ERROR + ": " + @SERROR
? "KiX Version: " + @KIX

Returns for me
Code:

Yeah
Error 0: The operation completed successfully.
KiX Version: 4.53

What do you get?