So, a bunch of people I've talked to (including me) have been having issues with a Skype error that says 'unexpected end tag: "b" actual "font"'. Now, it's not a problem, it's just annoying. After a quick google, the solution from the Skype forums stared me in the face. So, I decided to try it out, and it seems to have worked perfectly fine.
Go to "Tools-> Options -> Notification Settings -> Alerts and Messages" and just untick everything. Skype appears to be having a problem with parsing the HTML in its alerts recently, so just disabling them completely fixes it. I've yet to have any errors since.
EDIT: If this doesn't work, you might have to go to "Tools -> Options -> Advanced" and disable "Automatically start Extras".
Also, please note that this isn't a permanent fix. It's merely a workaround until the Skype developers find out what's gone wrong and what they have to do to stop it from happening in total.