Well, Split returns an array of strings, not an array of numbers, so you're doing string comparisons. This may not be valid. If you do something like:
Case Val($KSNR) >= 10
it should work.

Personally, I'd prefer something like:
 Code:
$KSArray = Split ($KSAnzahl,",")
For Each $KSNR in $KSArray
  If Val($KSNR) >= 0
    $POS = $Site + "POS" + Right("00" + $KSNR, 2)
    "Site is " $POS ?
  EndIf
Next

This can eliminate the Gosub, and will always left-pad your number with zeros to the length of two digits. The logic can be extended to perform padding to any length by increasing the string of zeros, and the desired string length.

Glenn
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Actually I am a Rocket Scientist! \:D