You may check if those folders already have a backslash.

if SUBSTR( lcSourceFolder, LEN(lcSourceFolder), 1) != "\"
    lcSourceFolder = alltrim(lcSourceFolder) + "\" 
endif
if SUBSTR( lcTargetFolder, LEN(lcTargetFolder), 1) != "\"
    lcTargetFolder = alltrim(lcTargetFolder) + "\" 
endif

So it will add the "\" only if it does not have it.