We upgrade to the 1.8 driver via NuGet this morning and instantly brought down our dev environment.

Here is part of the stack trace:

at System.Linq.Enumerable.Single[TSource](IEnumerable`1 source, Func`2 predicate)
at MongoDB.Bson.Serialization.BsonClassMap`1.ResolveExplicitProperty(MemberInfo interfaceMemberInfo, Type targetType)
at MongoDB.Bson.Serialization.BsonClassMap`1.GetMemberInfoFromLambda[TMember](Expression`1 memberLambda)
at MongoDB.Bson.Serialization.BsonClassMap`1.GetMemberNameFromLambda[TMember](Expression`1 memberLambda)

Here is some snippets that will show how to reproduce:

protected override void ConfigureClassMap(BsonClassMap<T> cm) {
cm.SetIdMember(cm.GetMemberMap(c => c.Id).SetRepresentation(BsonType.ObjectId));
}

..
where T : class, IIdentity, new() {
..

public interface IIdentity {
string Id

}

..

public class JobHistory : IIdentity {
public string Id

}
..