Custom Library - Validation Error


My automation process throwing app exception with reason The UiElement is no longer valid, to fix this, I have to update few selectors in a custom library as this functionality is written in a custom lib. After publishing the library and updating it with latest version, process stops with following error:

Error ERROR Validation Error System.NullReferenceException: Object reference not set to an instance of an object.
at CustomWorkflow.GetImplementation()
at System.Activities.Activity.OnInternalCacheMetadata(Boolean createEmptyBindings)
at System.Activities.Activity.InternalCacheMetadata(Boolean createEmptyBindings, IList1& validationErrors) at System.Activities.ActivityUtilities.ProcessActivity(ChildActivity childActivity, ChildActivity& nextActivity, Stack1& activitiesRemaining, ActivityCallStack parentChain, IList1& validationErrors, ProcessActivityTreeOptions options, ProcessActivityCallback callback) at System.Activities.ActivityUtilities.ProcessActivityTreeCore(ChildActivity currentActivity, ActivityCallStack parentChain, ProcessActivityTreeOptions options, ProcessActivityCallback callback, IList1& validationErrors)
at System.Activities.ActivityUtilities.CacheRootMetadata(Activity activity, LocationReferenceEnvironment hostEnvironment, ProcessActivityTreeOptions options, ProcessActivityCallback callback, IList`1& validationErrors)
at System.Activities.Validation.ActivityValidationServices.InternalActivityValidationServices.InternalValidate()
at System.Activities.Validation.ActivityValidationServices.Validate(Activity toValidate, ValidationSettings settings)
at System.Activities.Presentation.Validation.ValidationService.CoreValidationWork(ValidationReason reason, CancellationToken cancellationToken) Process.xaml

I did look forum
and replaced Select Item activity with Select Multiple Items but unfortunately no luck.

I did further research and publish the custom library without any changes to see the root cause and seems the process doesnt recognize the new lib version.

Any ideas/ thoughts please.

Hi @ramvashista85,

Could you, please, share the library project which generated this behavior?
We had a similar issue (which you’ve linked in your comment through the reference to the other Forum post) and it was fixed within the 19.10.4 release. For a quick fix solution, I would suggest trying to upgrade your setup to 19.10.4 or higher, if this is an option. If the upgrade is not possible or if it does not fix your issue, it would really help us to take a look into your library project.

Thank you

Hi @LiviuPonova , thank you for your response.
We are planning to upgrade uipath platform to 2020.10.X and hopefully this issue is not there.
Will keep posted once upgraded.

I had this issue today with a new custom library I created. We are on Orchestrator version 2020.10.4 but my Studio is only 2019.10.3. Replacing Select Item with Select Multiple Items solved the issue.

Is the issue with Studio itself or with the UiPath.System.Activities (v19.10.1) or UiPath.UiAutomation.Activities (v19.11.1)?