Share WIFI Internet via Bluetooth PAN
Your messages says it clearly.

Your Internet can not be shared! 

It is prohibited to do so by a set up called 802.1x.

Your network administrator(or you) has created the 802.1x configuration profile to connect to 802.1x type network.

That profile does not allow you to share wifi (for security reasons).

If you have access to the 802.1x then you can change that.

If you do not have access:

Try creating NEW Location ! (without the 802.1x configuration).

Under Apple(top left) select Location > Network preferences

In the new Network window click on the Location then select Edit..

Now click on the (+) to add new location (name it)

Now select (add with +)the wifi to use, and add Bluetooth PAN (with (+))

Now go to sharing and Enable Internet sharing with BT PAN.

Do not forget to turn off and turn on the WiFi to enable it.