Comment 3 for bug 745102

In preferences -> Appearance you can switch "Use tabbed interface" on and off.

I tried to reproduce the issue with both tabbed and non tabbed interface, but with both I was unable to get the error message. So due to your question I guess you use the tabbed interface.

Do you have any chat window open when you receive the error message when you get that error, or is coccinella opening a new window? When you have a chat window open, is there already a tab open for this contact, or is coccinella trying to open a new tab? In case there is a tab already, is it the active tab when you receive the error message?