Error when connecting via CacheExtreme

I'm following this guide as well as the sample.cs file and getting an error message on this line
cache_connection.Connect();

The error is:
Caught GlobalsException: lc_conn::connect_device returned Db_err: source: lc_conn::connect()  message: lc_conn::connect: CacheSecureStart returned -15: <ACCESSDENIED>

I've tried many variations of Namespace + Username + Password and they all result in that error, even though I can connect to the namespace just fine using other means.