Sometimes you got warning message like "Item cannot be more than 256 characters" at the people editor control while adding or updating large number of data. To avoid this just add below script to content editor web part & Change g_MAX_LEN
value as required.
<script language="ecmascript"
type="text/ecmascript">
function onPageLoad() {
g_MAX_LEN = 2000;
}
$(document).ready(onPageLoad);
</script>
Thanks & Regards
Modi Vishal