I've just started having an issue where I can't open a BBM msg from within the Hub. I have to go to the app, but even that is a bit slower than normal. I have a lot of available memory (or so I think), so hopefully that's not the reason for this.
I've got the same issue twice on both of our z10 .
it's a software bug.
Try to refresh hub as previous man said, then try to create new BBM message within hub. Possibly, it forces chat to open.