Rails 3 random database exceptions using postgres

One of our application is built on Rails 3 which uses postgres as database. We observe that while doing load test i.e continuously submitting request, there are random exceptions related to database (comes from postgres_adapter):

1. PG::Error: Wait on socket error (WaitForMultipleObjects):
2. NoMethodError: undefined method `result_error_field' for nil:NilClass: 

I am not able to find any reference on cause of these issues as they're coming at different points. Any help on how to avoid this or solve this would be helpful.

Thanks