Events fail randomly

[Dominguez]

Events in schedule work fine but some days all events fail with one of this erros:

CNC-MON-0036 Recovered from an unexpected server crash. The task history may not have been written completely.
CNC-SDS-0413 There was a problem in executing the task. The user authentication failed. It may not be possible to rerun the task.

What could be happening here? 

Thanks!

[AussiePete2011]

If its Cognos 8.4, its likely to be a known issue.
It's supposed to be fixed in 8.4.1 and 10

[Dominguez]

Yes, it is 8.4. 

Thanks!

[IceTea]

Do the events start on same time?

I had such an issue and planned the events one minute after another... worked ;o