Are you logged in as admin? If so go to yoursiteroot/Admin/PageTree.aspx
select your home page and click the pencil then select the Event Calendar Module and click the gear to get to instance settings.
If you are not logged in another solution is to edit the file at
/Setup/applications/STS_EventCalendarPro/FeatureDefinitions/40000_EventCalendarModulle.config
look for this:
<featureSetting
resourceFile="STSEventCal"
grouNameKey="DateTimeSettings"
resourceKey="TimeZoneIdSetting"
defaultValue=""
controlType="ISettingControl"
controlSrc="~/Controls/TimeZoneIdSetting.ascx"
helpKey="sts-eventcal-TimeZoneSetting-help"
sortOrder="1000"
regexValidationExpression=""
/>
and set the default value to:
Eastern Standard Time
Then visit the Setup page again.
Thats should get past the error then you can change it to a different time zone if needed. I'm adding that default for the next release , someone else just reported this problem yesterday.
Hope that helps,
Joe