Internet Sharing not working after update!

Hi,

So I'm at University and I've been sharing my internet from my macbook (connected via ethernet) to my iPhone.

It's been working fine, with me being able to access things from my phone (such as emails etc.) when I'm about the house or whatever.

However, since I recently updated the recent updates from apple whenever I try to share the internet it simply doesn't work, the connection states it's there and it appears in my iPhone's wifi list, I can seemingly connect to it and it shows I have full signal yet the signal doesn't work.

Also, it appears that it works again once I turn my macbook's firewall off, but I don't really want to be doing that.

Does anyone have an idea how to fix this or have any idea why it's suddenly started happening?

Thanks in advance,

Rob.