Okay, I'll summarize what we know :
empathy can't start a video call, and issues some kind of Gtk-CRITICAL error.
What does the error message tell us? Not much, I'm afraid, for it appears in various situations, according to a quick google search[1].
With this much, I don't think this can be easily solved. More info would be needed to debug this, though I don't know much about empathy and I can't say which piece of info would be needed.
Hopefully someone more knowledgeable than me will tell you which info you should provide, but bumping the topic every now and then won't help much. Somebody already posted the link to this topic on the mageia-discuss ML, and the answer was:
wobo wrote:My first idea would be to ask for information - the post does not contain any info at all.
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[1]
http://www.google.com/#sclient=psy&hl=en&site=&source=hp&q=gtk-critical+gtk_tree_model_filter_real_unref_node+empathy&aq=f&aqi=&aql=&oq=&pbx=1&bav=on.2,or.r_gc.r_pw.&fp=5014d35bb6efb157&biw=1280&bih=680