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The message indicates that there is some kind of syntax error with the passed uri once the relative NavigateUrl and BaseUrl values are combined. Does the navigate step itself have a BaseUrl value and/or have you set a project wide BaseUrl? With the limited information provided, I can only advise that you try to adjust these values in attempt to rectify the full uri address which gets passed in the navigate step. If you require additional assistance, please provide us with a copy of your project in a ZIP file which we can use to reproduce the problem.