Nope. The code works fine within the app, and it’s the same code, so I don’t think either of these is possible. Just to be complete, the function itself is about as simple as it gets:
In the server module:
@anvil.server.callable
def player_list():
return app_tables.players.search()
And in the code running on the foreign computer (as you see in the error message)
result = anvil.server.call('player_list')