• the amount of brackets in line 35 isn't correct.
• you try in last WHILE/LOOP structure to remove "," symbols, but you
  are removing SPACE character.
• you are using INTEGER which has a restrictive max/min value.
  As input we are using:
  

  code:

  ---

          19 file(s)  3,591,977,164 bytes
         214 file(s)     34,605,720 bytes
           1 file(s)         27,648 bytes
           3 file(s)        281,795 bytes
           3 file(s)          1,046 bytes
         240 file(s)  3,626,893,373 bytes

  ---

  the output becomes something like
  

  code:

  ---

   input          240 file(s)  3,626,893,373 bytes
   files   240
   bytes   3,626,893,373
   convert 3626,893,373
   convert 3626893,373
   convert 3626893373
   bytes   -652415

  ---

  the latest value of "-652415" will be use for calculation number of KBytes.
  

code:

---

 $path="h:\"
 $tempfile="c:\00003.tmp"

 $lokaal=GetFileVersion("%WINDIR%\Explorer.exe", "Language")
 IF ($lokaal = "0413Dutch")
       $string="bestand(en)"
 ELSE
       $string="File(s)"
 ENDIF
 ? "language "+$lokaal+" -> search for "+$string+" in directory "+$path
 ;
 ;=== Vang de DIR info op, filter alle regels weg behalve de regels met $String (directory output)
 ;
 SHELL '%comspec% /c dir "$path" /s /a-d /-c | find "$string" >$tempfile'
 ;
 IF (Open(1, $tempfile, 2) = 0)
       $line=ReadLine(1)
       WHILE ($line <> "")
             $prevline=$line
             $line=ReadLine(1)
       LOOP
       $=Close(1)
 ENDIF
 DEL $tempfile
 ;
 ? " input   "+$prevline
 $files=Val(Ltrim(Substr($prevline, 1, InStr($prevline, "f") - 2)))
 ? " files   "+$files
 $bytes=Ltrim(Substr($prevline,InStr($prevline,")")+1,Len($prevline)-InStr($prevline,")")-(Len($prevline)-InStr($prevline,"b")+2)))
 ? " bytes   "+$bytes
 WHILE (InStr($bytes,",") <> 0)
       $bytes=Substr($bytes,1,InStr($bytes,",")-1)+Substr($bytes,InStr($bytes,",")+1,Len($bytes)-InStr($bytes,", ")+1)
       ? " convert "+$bytes
 LOOP
 ;
 ;=== Converteer het resultaat naar een integer variable.
 ;
 ? " bytes"+Val($bytes)
 $homedir_kbytes=(Val($bytes)+512)/1024
 ? " KBytes  "+$homedir_kbytes

---