It is obvious that the error is due to virtual shadows, so sometimes it just helps to turn them off with the r.Shadow.Virtual.Enable 0
This error is related to the number of light sources, so you can try to remove the extra ones, or remove Cast shadows from them
It looks like the correct solution would be to increase this pool itself, similar to the problems with r.Streaming.PoolSize, but I personally did not find this command (selecting r.Shadow.Virtual.MaxPhysicalPages values not work for me)