did you upgrade it manually or using the rpms?
If you've upgraded manually, you'll probably also have to upgrade the Zope contents.
1. Check the setup
Assuming you've installed the software in /opt/schedulix, do a
-bash-4.2$ ls -l /opt/schedulix/schedulixweb/import/SDMS.zexp
lrwxrwxrwx. 1 schedulix schedulix 39 Jan 26 2017 /opt/schedulix/schedulixweb/import/SDMS.zexp -> /opt/schedulix/schedulix/zope/SDMS.zexp
Now if this looks different in your installation, you'll have to find your SDMS.zexp file first.
You might try to find it below /opt/schedulix/schedulix/zope or /opt/schedulix/schedulix-2.9/zope
After having found the SDMS.zexp file, you can create a link like above or copy the file to the Zope's import directory.
2. Open the management page
This is like the URL you use all the time, but instead of "SDMS" you write "manage"
3. Rename or Drop the SDMS folder
4. Import the new SDMS.zexp
After a refresh of the main desktop you should see the Interval editor.