I came across the same problem, and worked around it by checking async_load with ds_exists(async_load,ds_type_map). It's the only way I managed to stop the error from showing up.
At the start of the Social Asynchronous event, I put:
If true, I run the rest of the event code, otherwise I don't.
Game Maker's asynchronous event should never hold async_load without it being a map (not sure what else it is), but it occasionally happens as you said.