I also have the exact same issue on a fresh installation of Server 2008..!
I will try to revert to version 1.5.409.147 as well.
Update:
Reverting to 1.5.409.147 didn't help.
The <userSettings> in the config does contain the property:
<setting name="firstRunDate" serializeAs="String">
<value />
</setting>
So not sure what else to do? My log is;
14:01:9044 | Operating System: Microsoft Windows NT 6.0.6002 Service Pack 2
14:01:9094 | .NET version: 4.5.50709
14:01:9094 | BoxCryptor v1.5.409.147 started!
14:01:9124 | CFBS Driver v 4.0.129.5 installed, service is stopped
14:01:5356 | System.Configuration.SettingsPropertyNotFoundException: The settings property 'firstRunDate' was not found.
at System.Configuration.SettingsBase.GetPropertyValueByName(String propertyName)
at System.Configuration.SettingsBase.get_Item(String propertyName)
at System.Configuration.ApplicationSettingsBase.GetPropertyValue(String propertyName)
at System.Configuration.ApplicationSettingsBase.get_Item(String propertyName)
at BoxCryptor.Properties.Settings.get_firstRunDate()
at .(String[] )