Unexpected security validation error in SharePoint workflow

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1

I’m facing a strange security issue with my SharePoint workflow that has been bothering me. When executing certain tasks, I receive the following error message:

Microsoft.SharePoint.SPException: The security validation for this page is invalid.

Usually, when this error comes up in standard SharePoint development, I simply manage my code like this:

web.AllowUnsafeUpdates = true;
// your code to update here
web.AllowUnsafeUpdates = false;

However, this is the first instance of encountering this within a workflow, which is odd because workflows should have system-level access. The issue first arose when I tried to modify a field value in a custom code activity. Applying the AllowUnsafeUpdates fix did resolve it in that case.

Later, I encountered the same issue with a CreateTask activity, but it only happened in the MethodInvoking event handler. The stack trace consistently references SPListItem.UpdateItem failing specific security validations.

What complicates this issue is that my SharePoint development setup has been functioning smoothly for several months. All my other projects and workflows work as expected, suggesting it’s not a configuration issue. It seems to be something unique to this particular workflow causing the problem.

I managed to circumvent the issue by starting a new project from scratch and rebuilding it. But I still have the original flawed project and I’m eager to find out what the problem was. Has anyone experienced a similar situation?

2

Sounds like workflow context corruption - I’ve hit this before. AllowUnsafeUpdates working at first then breaking in different activities means the workflow’s security context got messed up during development. This happens with partial deployments or when old assembly references stick around from previous builds. Check your GAC for duplicate or stale workflow assemblies - Visual Studio’s terrible at cleaning these up during debug sessions. Also look for any custom auth or impersonation code that might mess with the workflow’s elevated privileges. The CreateTask activity problem screams threading context issue where the security token isn’t inheriting properly. Try a full retract and redeploy instead of just rebuilding - usually clears these phantom security errors.