Events stopped running

[Gogs]

A couple of days ago events stopped triggering, a re-boot sorts the problem for a couple of hours, here is an extract frfom the latest log

29/04/2016 23:05:10 Error Kitchen Movement Sensor On Pre Midnight After Dusk EventProcess error 91: Object reference not set to an instance of an object.
29/04/2016 23:05:10 Error In ProcessEventItem, setting up to thread event: Object reference not set to an instance of an object. at 0
29/04/2016 23:05:10 Error Kitchen Movement Sensor On Pre Midnight After Dusk EventProcess error 91: Object reference not set to an instance of an object.
29/04/2016 23:05:18 Error In ProcessEventItem, setting up to thread event: Object reference not set to an instance of an object. at 0
29/04/2016 23:05:18 Error Kitchen Movement Sensor On Pre Midnight After Dusk EventProcess error 91: Object reference not set to an instance of an object.
29/04/2016 23:05:18 Error In ProcessEventItem, setting up to thread event: Object reference not set to an instance of an object. at 0
29/04/2016 23:05:18 Error Kitchen Movement Sensor On Pre Midnight After Dusk EventProcess error 91: Object reference not set to an instance of an object.
29/04/2016 23:05:24 Error In ProcessEventItem, setting up to thread event: Object reference not set to an instance of an object. at 0
29/04/2016 23:05:24 Error Kitchen Movement Sensor On Pre Midnight After Dusk EventProcess error 91: Object reference not set to an instance of an object.
29/04/2016 23:05:24 Error In ProcessEventItem, setting up to thread event: Object reference not set to an instance of an object. at 0
29/04/2016 23:05:24 Error Kitchen Movement Sensor On Pre Midnight After Dusk EventProcess error 91: Object reference not set to an instance of an object.
29/04/2016 23:05:31 Error In ProcessEventItem, setting up to thread event: Object reference not set to an instance of an object. at 0
29/04/2016 23:05:31 Error Kitchen Movement Sensor On Pre Midnight After Dusk EventProcess error 91: Object reference not set to an instance of an object.
29/04/2016 23:05:31 Error In ProcessEventItem, setting up to thread event: Object reference not set to an instance of an object. at 0
29/04/2016 23:05:31 Error Kitchen Movement Sensor On Pre Midnight After Dusk EventProcess error 91: Object reference not set to an instance of an object.
29/04/2016 23:05:45 Error In ProcessEventItem, setting up to thread event: Object reference not set to an instance of an object. at 0
29/04/2016 23:05:45 Error Kitchen Movement Sensor On Pre Midnight After Dusk EventProcess error 91: Object reference not set to an instance of an object.
29/04/2016 23:05:45 Error In ProcessEventItem, setting up to thread event: Object reference not set to an instance of an object. at 0
29/04/2016 23:05:45 Error Kitchen Movement Sensor On Pre Midnight After Dusk EventProcess error 91: Object reference not set to an instance of an object.
29/04/2016 23:06:04 Error In ProcessEventItem, setting up to thread event: Object reference not set to an instance of an object. at 0
29/04/2016 23:06:04 Error Kitchen Movement Sensor On Pre Midnight After Dusk EventProcess error 91: Object reference not set to an instance of an object.
29/04/2016 23:06:04 Error In ProcessEventItem, setting up to thread event: Object reference not set to an instance of an object. at 0
29/04/2016 23:06:04 Error Kitchen Movement Sensor On Pre Midnight After Dusk EventProcess error 91: Object reference not set to an instance of an object.
29/04/2016 23:06:13 Error In ProcessEventItem, setting up to thread event: Object reference not set to an instance of an object. at 0
29/04/2016 23:06:13 Error Kitchen Movement Sensor On Pre Midnight After Dusk EventProcess error 91: Object reference not set to an instance of an object.
29/04/2016 23:06:13 Error In ProcessEventItem, setting up to thread event: Object reference not set to an instance of an object. at 0
29/04/2016 23:06:13 Error Kitchen Movement Sensor On Pre Midnight After Dusk EventProcess error 91: Object reference not set to an instance of an object.
29/04/2016 23:06:21 Error In ProcessEventItem, setting up to thread event: Object reference not set to an instance of an object. at 0
29/04/2016 23:06:21 Error In ProcessEventItem, setting up to thread event: Object reference not set to an instance of an object. at 0

Any ideas what the problem is?

thanks.