Changing the scheduler to timer mode does nothing to stop these errors. I have been running in timer mode for months and scheduler errors keep piling up. I clear all my logs daily to keep them small, so this isn't the cause. It's very clear that there is something else going on here. Why webserver table is also fine. This issue started right after an upgrade around 5.2.

We need a proper explanation and fix for this. This issue has nothing to do the size of the log or the load on the database and the error are getting frustrating.

Im still seeing this is both 5.6.0 and 5.6.1 systems - both on sites that are upgrades from earlier versions and on new sites as well.

Westa

OK so I've been struggling with this issue the past couple of days. I've tried everything in this thread and more, and finally I took a closer look at the code that I wrote for my custom scheduler item. I was calling the "Completed()" function on the SchedulerClient base within my custom scheduled item, thinking that was appropriate given examples I've seen elsewhere call "Errored()" and "Progressing()". My fix was simple: Remove calls to the "Completed()" sub. This addressed the issue in my case. This may be way off, I haven't inspected DNN source code or stepped through DNN code (tough to do anyways with threading issues like this), so I may be like others in this forum topic thinking the issue is resolved only to see it rear it's ugly head in the future. That said, the same problem happened consistently until I removed the call to Completed()...and I do agree that whatever the root cause of this issue, the side-effects of this have only surfaced recently. I upgraded DNN 5.5.4 to DNN 5.6.1 and started running into this...so somewhere in between those two releases, the behavior of the core scheduler processing code seems to have changed. I do hope this info helps someone out there. I know how frustrating it is to be stuck on an issue. I've got ASDF imprinted on my forehead from this particular issue. Work hard & play hard, my friends! -C