Over the past few weeks, I've had trouble adding comments on this site and others.  In the past week, I've heard from two friends that they're having trouble as well.  I talked to the help center last night, and they tell me that it is related to an individuals browser settings.  They recommend clearing out browser cache and cookies, updating your web browser and disabling pop ups.  I don't know if it will work, but thought I'd pass it on.