Unable to install the Golf Cart demo data

Hi,

I'm trying to install the Golf Cart demo data into our Windchill 11.0 instance. Obviously, something wrong happens.

From a windchill shell, I run: windchill wt.load.WindchillLoader -LoadOnlyDemo

And I get the following stack trace:

Welcome to Database Setup Utility for Windchill and Windchill Solutions.

You will be presented with a series of prompts.
If you have already installed a base data set as part of a previous
loading sequence you do not need to load it again.
----------------------------------------------------------------
Stop the ServerManager.
NOTE: If the SM is hung on the MethodServer, this may wait for 60 sec.
NOTE: If the SM is not running, you'll get a traceback ending in
 java.net.ConnectionException: Connection refused
 This can be ignored.
Begin stop sequence...
----------------------------------------------------------------
Checking if MethodServer is alive
Server Manager is not running
----------------------------------------------------------------
Start the server manager ....
2018-10-11 16:47:43,602 WARN [main] wt.manager.ServerLauncher - Starting ServerManager
Make sure it's running ...
ServerManager is alive!!
Windchill service (MethodServer) starting (1) instance(s)
wt.util.WTException: Unable to connect to your web server.
Attempts to read the URL https://<our wc 11.0 server>/Windchill/servlet/WindchillGW/wt.httpgw.HTTPServer/ping failed.

Nested exception is: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building
failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested
 target
 at sun.security.ssl.Alerts.getSSLException(Alerts.java:192)
 at sun.security.ssl.SSLSocketImpl.fatal(SSLSocketImpl.java:1949)
 at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:302)
 at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:296)
 at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1509)
 at sun.security.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:216)
 at sun.security.ssl.Handshaker.processLoop(Handshaker.java:979)
 at sun.security.ssl.Handshaker.process_record(Handshaker.java:914)
 at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:1062)
 at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1375)
 at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1403)
 at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1387)
 at sun.net.www.protocol.https.HttpsClient.afterConnect(HttpsClient.java:559)
 at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java
:185)
 at sun.net.www.protocol.https.HttpsURLConnectionImpl.connect(HttpsURLConnectionImpl.java:153)
 at wt.load.Installer.isServerUp(Installer.java:721)
 at wt.load.Installer.startupComplete(Installer.java:630)
 at wt.load.Installer.checkServiceStartup(Installer.java:678)
 at wt.load.Installer.startServerManager(Installer.java:453)
 at wt.load.BasicLoader.doInstall(BasicLoader.java:285)
 at wt.load.BasicLoader.<init>(BasicLoader.java:207)
 at wt.load.WindchillLoader.load(WindchillLoader.java:359)
 at wt.load.WindchillLoader.main(WindchillLoader.java:462)
Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertP
athBuilderException: unable to find valid certification path to requested target
 at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:387)
 at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:292)
 at sun.security.validator.Validator.validate(Validator.java:260)
 at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:324)
 at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:229)
 at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:124)
 at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1491)
 ... 18 more
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to reques
ted target
 at sun.security.provider.certpath.SunCertPathBuilder.build(SunCertPathBuilder.java:141)
 at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:126)
 at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:280)
 at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:382)

Any help would be appreciated. Thanks.