Once during a run last night and once just sitting there connected to the dome, scope, camera and weather a few minutes ago with the following error:

Run-time error '-2147467261 (80004003)
Object reference not set to an instance of an object.

It has run flawlessly for a a week before this.

This usually means a dependent ASCOM driver may have crashed. This is ACP 6.0 build 11 with hotfix 4.0. There are no system or application error events in the eventvwr.

Any ideas?