Same problem here, with an account at jabber.fr, impossible to connect since the update to stretch. Worked fine before, works fine on other computers.
Attached is a screenshot of the error.
Also if I start kopete in the console I get this output:
QDBusConnection: session D-Bus connection created before QCoreApplication.
Application may misbehave.
QDBusConnection: session D-Bus connection created before QCoreApplication.
Application may misbehave.
kopete(13034)/kdecore (KLibrary) kde4Factory: The library
"/usr/lib/kde4/kopete_history.so" does not offer a qt_plugin_instance function.
kopete(13034)/libkopete Kopete::PluginManager::loadPluginInternal: Unable to
find a plugin named ' "" '!
Unknown signature value: 795
Unknown signature value: 795
Unknown signature value: 795
Unknown signature value: 795
Unknown signature value: 795
Unknown signature value: 795
Unknown signature value: 7
Unknown signature value: 795
Unknown signature value: 795
Unknown signature value: 794
Unknown signature value: 795
Unknown signature value: 795
Unknown signature value: 795
Unknown signature value: 794
Unknown signature value: 795
unexpected version response
