Hello,
Firstly and foremost update Joomla! immediately you are at a immediate risk of being hacked V2.5.17 is extremely insecure and really so is 2.5.28. You should be on 3.6.5.
Jevents 3.2 is very old now but try this CSS:
.ical_dialogJQ.modal.hide.fade.in {
z-index: 999999 !important;
}
Failing that you need to update JEvents to V3.4.25 but to do that you need Joomla! 3.6.
Many thanks
Tony