MongoDB C# driver WriteConcernException Unauthorized on writes for readOnly=false user - mongodb

Question

I've been running my application with a readOnly=false admin user for 6 months in development on MongoDB 2.2.2. We're getting closer to launch and I wanted to switch over the user that my application runs under to a user in the application's database only with readOnly=false.
I ran the following script from the robomongo as the admin user.
use MyDB
db.addUser("api", "MyPassword", {"readOnly": false});
I also updated the MongoDB connection string to the following.
<add key="DataServer" value="mongodb://api:MyPassword#localhost:27017/MyDB" />
It created my user correctly and I validated that it is in MyDB and is readOnly=false. However, when I use the MongoDB c# driver 1.8.1 it fails on any writes with a WriteConcernException unauthorized. I am able to read records just fine from the database. Looking at the MongoDB logs it is correctly logging into my DB from my c# application but failing on the write calls.
Using the robomongo shell I was able to successfully auth with the api user and write records into one of the collections in the application's DB. So it's leading me to believe that it's something to do with the c# driver. I've also debugged my application code and validated that the MongoClient's GetServer method is returning a MongoServer that has the correct credentials.
Here's the robomongo shell script I ran to validate the user is able to write to the DB.
use MyDB
db.auth("api","MyPassword");
db.Person.insert({"first_name":"Test","last_name":"User"});
db.Person.find({"first_name":"Test"});
Any help as to why the MongoDB c# 1.8.1 driver connecting to MongoDB 2.2.2 and not being able to write records in a user DB with a readOnly=false user would be greatly appreciated.

Answer 1

I can't really see much wrong with your code. I'd suggest trying the following:
Make sure you're reading the DataServer app setting correctly in your C# code (including the DB name)
Create the user in the admin database and see if that helps:
use admin
db.addUser("api", "MyPassword"); // readonly defaults to false