Topic
After installing the SharePoint Server Subscription Edition October 2026 CU (Feature Update 26H2), customers may experience failures with Nintex Scheduled Workflows. Scheduled workflows fail to start and generate errors related to workflow rule deserialization.
This issue is caused by a SharePoint change introduced in the October 2026 update and is not specific to Nintex Workflow configuration.
The following error may be observed in the SharePoint ULS logs:
RunWorkflow Exception: Microsoft.SharePoint.Workflow.SPDeclarativeWorkflowRulesBlockedException:
Declarative workflow blocked: rules resource 'ROOT.rules' could not be fully deserialized.
System.Workflow.ComponentModel.Serialization.WorkflowMarkupSerializationException:
CreateInstance failed for type 'System.Workflow.Activities.Rules.RuleDefinitions'.
Object reference not set to an instance of an object.
Instructions
Resolution
Run the following SharePoint PowerShell commands on a SharePoint server within the farm:
After applying the change, re-test the scheduled workflows to confirm they are executing successfully.
Additional Information
Reference
Microsoft MVP Stefan Goßner has documented this SharePoint issue and the recommended workaround in the following article: