I have been looking for a solution on the internet before asking for your help here.
My drupal site was working fine since yesterday when I create a calendar event chain ( this is a custom module) and i clicked "save", then this error appeared:
I have checked from the recent log message and found this
I dont know what have happened since I cleared all the queuing using queue manager. The funny thing is that if I use the backup database, which had backed up before this error happened from the production site to my localhost, then everything works fine and I am able to create the even and save it. So is there any problem with the database ? I wish i could use the backup database on my production site ? :/
Thank you for your replies.