A recent security vulnerability on Java prompted Oracle to release critical patches for the JDK in versions 6u101, 7u85 and 8u51.
This upgrade prevented OMERO clients from connecting to the server. A fix for this issue is now available, you should upgrade your Java version to take advantage of the security fix and refer your system administrator to
for details of how to patch your server. You do not need to download new clients and this fix will also be included in the next release of OMERO (5.1.3).
— July 22, 2015