If secure access is setup for Mingle then the following should be considered when upgrading Mingle:
1. Ensure that the keystore file is moved to the new folder structure associated with new version. Say you were migrating from 3.3 to 3.4 then it is possible that the keystore is lying in one of the 3.3 sub folders. Move it to equivalent sub folder under Mingle 3.4
2. Update mingle.properties with the new path to the keystore (after step #1)
3. Depending on the SSL tool used to create certificate, there could be more SSL files lying in the MINGLE_INSTALL_DIR/jre/bin of the old version. This is more true of Windows because we ship the JVM along with the Windows version. Every install of Mingle comes with own jre/bin. A Linux/ Othe_OS install will not have this problem because it will most likely continue to point to the same jre/bin as before the upgrade.
Move all SSL files from jre/bin folder of earlier version to the jre/bin of the new version.
4. Restart Mingle server for it to be able to find the SSL files in new folders.