Getting 'Value cannot be null. (Parameter 'g')' when running projekt from Assistiant

Feedback Robot
1

In Studio/robot version 2025.10.14 (Stand alone),
when running ANY projekt from Assistant I get this error: Value cannot be null. (Parameter ‘g’)
(Also in a new projekt with just a ‘Write line’ - and only the UiPath.system.Activities packages installed)

In Studio/robot version 2025.10.11 - I don’t get the error.
but in version 2025.10.12, .13 and .14 I get: Value cannot be null. (Parameter ‘g’)

Error details:

Value cannot be null. (Parameter ‘g’)

at System.ArgumentNullException.Throw(String paramName)
at System.Guid..ctor(String g)
at UiPath.Plugin.Activities.Tracing.ActivityTraceClient.g__PrepareForEnqueue|14_0(TraceSpan span, <>c__DisplayClass14_0&)
at UiPath.Plugin.Activities.Tracing.ActivityTraceClient.SubmitSpanInternal(TraceSpan span, Nullable1 status, Nullable1 endTime)
at UiPath.Plugin.Activities.Tracing.ActivityTraceClient.SubmitSpan(TraceSpan span, StatusEnum status, Nullable1 endTime) at UiPath.Plugin.Activities.Tracing.Tracer.CreateRootSpan(Guid jobId) at UiPath.Plugin.Activities.Tracing.ActivityTracingWorkflowInstanceExtension.SetInstance(WorkflowInstanceProxy instance) at System.Activities.Hosting.WorkflowInstance.InitializeCore(IDictionary2 workflowArgumentValues, IList`1 workflowExecutionProperties)
at System.Activities.WorkflowApplication.EnsureInitialized()
at System.Activities.WorkflowApplication.Enqueue(InstanceOperation operation, Boolean push)
at System.Activities.WorkflowApplication.SimpleOperationAsyncResult.Run(TimeSpan timeout)
at System.Activities.WorkflowApplication.BeginRun(AsyncCallback callback, Object state)
at UiPath.Executor.RobotRunner.RunWorkflow()

3

Hi @MarkDSVT

Clear %localappdata%\UiPath\Traces.Sign out and sign back into Assistant.
If not work Repair/reinstall Robot 2025.10.14.
As a workaround, stay on 2025.10.11 until a fix is released.

Happy Automation

4

I’m using Assistant in offline mode (i don’t have Orchestrator)
and don’t have a Traces folder in %localappdata%\UiPath\
and I have already tried to uninstall - only 2025.10.11 works - not 2025.10.12, .13, .14

5

@MarkDSVT

As per error and what youa re mentioning looks like its not able to get the latest package it needs

may be 25.10.11 was your previous version which already has the package that you are referring

cheers

6

Hi @MarkDSVT,

Try these options if these works:

  • Can you try to create and run a simple project from Studio. Check if the workflow executes from Studio, or only fail from Assistant?
  • Clear local UiPath cache. Try removing/renaming: %localappdata%\UiPath and %appdata%\UiPath
  • Repair or reinstall 2025.10.14. Sometimes configuration files survive upgrades.

Cheers!

7
  • All projects (even a simple one) works Studio - and only fails from Assistant
  • Clearing cache / reinstall didn’t help
  • Version 2025.10.11 works - Version 2025.10.12, .13 & .14 fails
9

Looking at the details here, this seems to be consistent with a bug that the engineering team recently addressed on S198. I’ve looped in my colleague, @Alexandru_Bizon , to bring more details.

10

In the meantime, as a workaround, you can downgrade to 25.10.11 while the team works on a fix for 25.10