Bug: UiBrowser cannot be passed as an argument in parallel, isolated workflows

Hi together

Invoke a worklow isolated, in a parallel activity, and pass it an UiBrowser. You will get an error as soon as you try to work with the variable in the invoked workflow. I haven’t tried it, but I think this happens with all Ui-variable types. The studio version doesn’t matter.

Please use the xaml to reproduce. Bug reports.zip (3,4 KB)

  "name": "BlankProcess",
  "description": "Blank Process",
  "main": "Main.xaml",
  "dependencies": {
	"Microsoft.Activities.Extensions": "[]",
	"UiPath.System.Activities": "[20.4.0]",
	"UiPath.UIAutomation.Activities": "[20.4.1]"
  "webServices": [],
  "schemaVersion": "4.0",
  "studioVersion": "",
  "projectVersion": "1.0.0",
  "runtimeOptions": {
	"autoDispose": false,
	"isPausable": true,
	"requiresUserInteraction": true,
	"supportsPersistence": false,
	"excludedLoggedData": [
	"executionType": "Workflow"
  "designOptions": {
	"projectProfile": "Developement",
	"outputType": "Process",
	"libraryOptions": {
	  "includeOriginalXaml": false,
	  "privateWorkflows": []
	"fileInfoCollection": []
  "expressionLanguage": "VisualBasic"

Thanks for your report, we will investigate.

Hi @Enrico

Our team had a look and it would seem like the UIBrowser object type is not serializable and it cannot be passed across isolated workflows.

It was further edited into our documentation: