Why does my BBM freez when I try to add or decline someone's invite?

I have restarted my phone loads of times, still nothing, I have updated my BBM to the latest....(10.8.5.15) Still nothing! When BBM does stop, I close the app and open it again and it works perfectly fine, until I try and add or decline someone's invite again! This has been happening for ages now, and I cant seem to fix it. I have a blackberry Z10.

If someone has a idea of what to do an how to fix this as nothing else of what other people have suggested works?