exec("/usr/bin/convert ".$tiffPath.$ref.".tiff  ".$CommonPath.$sourcePath.$ref.".jpeg");

// Ok until here

if (!file_exists($CommonPath.$destinationPath.$ref.".jpeg"))
{
    $executa = "/usr/bin/convert -size 800x800 ".$CommonPath.$sourcePath.$ref.".jpeg -thumbnail 800x800 ".$path.$destinationPath.$ref.".jpeg";

    exec($executa);
}

convert: unable to open image $CommonPath.$destinationPath.$ref.".jpeg": File is too big @ error/blob.c/OpenBlob/2589.