OK. So it seems that 128 MB RAM is not enough for your Moodle site. Please consider raising it to, say, 160 MB in your php.ini. That might help.
WRT the perpage thing, you can try something like
http://your.moodle.site/mod/workshop/allocation.php?cmid=XX&method=manual&perpage=10&sesskey=YYYYY where XX is the course module id of your workshop (same number that is passed as the 'id' parameter when viewing the Workshop) and YYYYY is your current sesskey (the easiest way to get know it is to search for the "sesskey" inside the HTML source of some in your browser).
SELECT * FROM mdl_user_preferences WHERE name='workshopallocation_manual_perpage';