Steps to reproduce: Install Debian 7 x86_64 add the 10gen repo apt-get install mongodb-10gen=2.2.5 Enable auth = true in /etc/mongodb.conf /etc/init.d/mongodb restart Create the test database: > use admin > db.addUser("admin", "admin") > use testdb > db.addUser("testuser", "testpass") Get the mongodb-src-r2.2.5.tar.gz tarball Compile only the client with the following command: scons --use-system-boost --release mongoclient Compile the following simple C++ test.cpp program: test.cpp #include <iostream> #include <string> #include <mongo/client/dbclient.h> using namespace std; int main() { mongo::DBClientConnection connection; string host = "localhost:27017" ; connection.connect(host); string error; connection.auth( "testdb" , "testuser" , "testpass" , error, true ); cout << "Auth: " << error << endl; mongo::BSONObj obj = BSON( "name" << "Dummy text" ); connection.insert( "testdb.unittest" , obj); error = connection.getLastError(); cout << "insert getLastError(): " << error << endl; connection.query( "testdb.unittest" , BSON( "name" << "Dummy text" )); error = connection.getLastError(); cout << "query getLastError(): " << error << endl; return 0; } g++ test.cpp -lmongoclient -lboost_filesystem -lboost_thread -lboost_system Run a.out Current result: $ ./a.out Auth: insert getLastError(): getLastError command failed: need to login query getLastError(): getLastError command failed: need to login Expected result: $ ./a.out Auth: insert getLastError(): query getLastError(): Some notes: The {{ {"name": "Dummy text"} }} object will be actually inserted into the database each time when the program is run, so getLastError() should NOT return error. Version 2.2.3 inclusive works fine. Between version 2.2.3 and 2.2.4 there were changes in the authentication table implementation. Versions 2.4.x seems to be fine as well.