Ls01rif($_REQUEST['marking_period_id']!='-1')
$max_term_RET = DBGet(DBQuery("SELECT MAX(SORT_ORDER) as MAX_SORT_ORDER FROM ".GetMP($_REQUEST['marking_period_id'],'MP_TABLE')." WHERE SYEAR='".UserSyear()."' AND SCHOOL_ID='".UserSchool()."'"));Похоже, что ф-ция возвращяет пустое значение, т.к.
Ls01rвот что пишет в ответ

[0]=>
&string(83) "SELECT MAX(SORT_ORDER) as MAX_SORT_ORDER FROM__WHERE SYEAR='2008' AND SCHOOL_ID='1'"
[1]=>
&string(18) "DB Execute Failed."
[2]=>
&string(168) "ERROR: syntax error at or near "WHERE"
LINE 1: SELECT MAX(SORT_ORDER) as MAX_SORT_ORDER FROM WHERE SYEAR='...