Change it from this:

<input type="text" class="form-textbox validate[required, Numeric]" id="input_5" name="q5_nricNo" size="20" maxlength="12" />

to this:

<input type="text" class="form-textbox validate[required, Numeric]" id="input_5" name="q5_nricNo" size="20" maxlength="12" onblur="mustBe12();" />