If the variable selectedValueDisplay is null (which it appears to be) then the jqery selector:
$("select[Title=Plans selected values']")
is not finding anything. If that selector doesnt work, we cant find the select control and nothing will work.
can you do a view source on your page and find the select box whose title is 'Plans selected values'?
Copy the 10 lines above and below it and paste it here and we can figure out why that selector is not working.