I found the problem. In the Permission records for your project there was a record for a non-existing role. Probably you have deleted some role at some point and the operation did not fully completed(something happened on our servers). The role itself was deleted successfully, but the associated permission records were not. This is why on loading of the Permissions screen the system was looking for the Name of a non-existing role, hence the error.
I fixed the problem, I just needed to create a fake role and then delete it. On deletion of a role all permission records are checked and optimized, which removed the orphaned records and the problem should now be fixed.
Can you please test now and see if everything works properly?
Sorry for the inconvenience.