Npgsql 2.1.2 is out! This is a bug fix release. Two fixes are present: KeyNotFoundException when setting ApplicationName on NpgsqlConnectionStringBuilder and A regression when using NHibernate with queries containing '<' operator. (Less Than' prepare failing). Unfortunately, this fix breaks previous support for @@ operators. So if you need this support, you will have to use the previous 2.1.1 version. Glen Parker is working in a permanent fix. Sorry for this big inconvenience. More info about that can be found at the link above. Please, give it a try and let me know if you have any problems. Please, report your issues in our github issues page .