MS Internet Explorer introduced new enhanced security features. You may need to make adjustments for CMEW to work.
First, apply efix150324 for an expired security certificate
Try upgrading to JAVA 1.6. One site reported that this resolve many of the issue he experienced with IE 11 upgrade.
When upgrading to MS Internet Explorer 11, you may need to change browser defaults to run with Endevor Change Manager Enterprise Workbench 12.0. Under 'Tools (Alt+x)' select 'Developer Tools'. Next pick the dropdown for 'Emulation'. Under 'Browser Profile', select 'Enterprise' and save. Depending on what other overrides you had made on your earlier IE versions, you may also need to change other defaults (ie. add your EW server as a trusted site etc.).