Problem installing gcal-persistence

System: Openhab 2.1

I am trying to install Google Calendar Presence Simulator binding but after clicking on ‘Install’ button on ‘Google Calendar Presence Simulator’ under Paper UI --> Add ons --> Persistence, I am getting the following on the log viewer:

2017-10-08 13:55:19.703 [WARN ] [gcal.internal.GCalPersistenceService] - gcal-persistence:calendar_name must be configured in openhab.cfg. Calendar name or word "primary" MUST be specified

==> /var/log/openhab2/events.log <==

2017-10-08 13:55:19.769 [ExtensionEvent            ] - Extension 'persistence-gcal' has been installed.

==> /var/log/openhab2/openhab.log <==

2017-10-08 13:55:20.147 [ERROR] [core.karaf.internal.FeatureInstaller] - Failed uninstalling 'openhab-misc-gcal1': Feature named 'openhab-misc-gcal1/0.0.0' is not installed

However, two config files are created in
the gcal-persistence.cfg and gcal.cfg

I entered the needed information in the above two files
(calendar_name in gcal-persistence.cfg
and client_id, client_secret and calendar_name in gcal.cfg)

I also created gcal.persist that contains:

Strategies {
default = everyChange

Items {
gPerSim* : strategy = everyChange

The log shows:

2017-10-08 14:06:24.230 [INFO ] [b.core.service.AbstractActiveService] - Google Calendar Event Downloader has been started

2017-10-08 14:06:42.427 [WARN ] [el.core.internal.ModelRepositoryImpl] - Configuration model 'gcal.persist' has errors, therefore ignoring it: [1,1]: mismatched input '<EOF>' expecting 'Strategies'

2017-10-08 14:06:42.455 [INFO ] [el.core.internal.ModelRepositoryImpl] - Loading model 'gcal.persist'

After that I restarted Openhab, the log shows:

2017-10-08 14:14:16.516 [INFO ] [core.karaf.internal.FeatureInstaller] - Uninstalled ‘openhab-persistence-gcal’

==> /var/log/openhab2/events.log <==

2017-10-08 14:14:16.520 [ExtensionEvent ] - Extension ‘persistence-gcal’ has been uninstalled.

Also the Paper UI shows that Google Calendar Presence Simulator is UN-installed

Any idea about what goes wrong here?