iCal4j Principles not found

Question

We are trying to connect to our instance of the CalendarStore but we don't understand the exception, that we get back when executing the code. The Error we're having:

org.codehaus.groovy.runtime.InvokerInvocationException: net.fortuna.ical4j.connector.ObjectStoreException: net.fortuna.ical4j.connector.FailedOperationException: Principals not found

We also know that the error occurs in line 62. Please note that I have edited the strings in the variables to not expose them to the public.

import com.github.caldav4j.CalDAVCollection;

import com.github.caldav4j.CalDAVConstants;
import com.github.caldav4j.exceptions.CalDAV4JException;
import com.github.caldav4j.methods.CalDAV4JMethodFactory;
import com.github.caldav4j.methods.HttpGetMethod;
import com.github.caldav4j.model.request.CalendarQuery;
import com.github.caldav4j.util.GenerateQuery;

import net.fortuna.ical4j.connector.ObjectStoreException;
import net.fortuna.ical4j.connector.dav.CalDavCalendarCollection;
import net.fortuna.ical4j.connector.dav.CalDavCalendarStore;
import net.fortuna.ical4j.connector.dav.PathResolver;

import org.apache.commons.codec.binary.Base64;
import org.apache.http.*;
import org.apache.http.auth.AuthScope;
import org.apache.http.auth.UsernamePasswordCredentials;
import org.apache.http.client.CredentialsProvider;
import org.apache.http.conn.routing.HttpRoute;
import org.apache.http.conn.routing.HttpRoutePlanner;
import org.apache.http.impl.client.BasicCredentialsProvider;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.conn.DefaultRoutePlanner;
import org.apache.http.impl.conn.DefaultSchemePortResolver;
import org.apache.http.protocol.HttpContext;

import net.fortuna.ical4j.model.Calendar;
import net.fortuna.ical4j.model.Component;
import net.fortuna.ical4j.model.ComponentList;
import net.fortuna.ical4j.model.component.VEvent;
import net.fortuna.ical4j.model.Date;
import net.fortuna.ical4j.data.CalendarBuilder;
import net.fortuna.ical4j.data.ParserException;
import net.fortuna.ical4j.connector.CalendarStore;

import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.impl.client.HttpClients;

import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.util.Iterator;
import java.util.List;


String USER = "User";
String PASS = "dont matter";


g_log.info("Start");

String uri = "our uri";

String prodId = "hm";
URL url = new URL("Our url");
PathResolver pathResolver = PathResolver.CHANDLER;

CalendarStore<CalDavCalendarCollection> calendarStore = new CalDavCalendarStore(prodId, url, pathResolver);

boolean testCon = calendarStore.connect(USER.toString(), PASS.toCharArray());

g_log.info("testCon: "+ testCon);