"ICE negotiation failed" refers to Globus Connect Personal's use of the STUN and ICE protocols to do "NAT hole punching".
In short, these are protocols for traversing a NAT device, typically something like a home router, and establishing peer-to-peer connections between two Globus Connect Personal endpoints.
If you're getting errors related to this, it strongly suggests that your network topology does not allow ICE to create a connection between the Globus Connect Personal endpoints you're using.
If you're testing a new setup, you can try to test transfers with Globus Tutorial Endpoint 1, Globus Tutorial Endpoint 2, or any other Globus Connect Server endpoint, you'll find that you've eliminated this source of potential errors. That's because Globus Connect Personal will simply make outbound connections to Globus Connect Server and doesn't need to try to use ICE.
In order for two Globus Connect Personal Endpoints to connect to one another using ICE, they need to be able to communicate with one another using UDP on ephemeral ports.
You can see a detailed document on the ports which are needed by Globus Connect Personal here:
The requirement for Outbound UDP 32768-65535 refers to the use of ephemeral ports.
If you have more questions, please don't hesitate to ask, but I hope this helps you get started.