We have encountered this bug also, even though we always have more than one step.  However, our steps are created dynamically.  The bug appears to be some sort of race condition when the page is being rendered.  We put inthis code to get around the race condition:

        <TelerikStepper Orientation="StepperOrientation.Vertical"
                        StepType="StepperStepType.Labels"
                        ValueChanged="@OnStepChange"
                        Value="@CurrentStepIndex">
            <StepperSteps>
                @{ // There is a bug in the TelerikStepper control that causes a
                    // crash "ArgumentException: The 'Max' value should be greater than 0'.  The crash occurs if there
                    // are zero or 1 steps defined.  What follows is a hack to get around that bug.
                    if (Data == null || Data.Count == 0)
                    {
                        <StepperStep Text="AA">
                            <Template>
                                <div>Step A</div>
                            </Template>
                        </StepperStep>
                        <StepperStep Text="B">
                            <Template>
                                <div>Step B</div>
                            </Template>
                        </StepperStep>
                    }   // End of hack
                }
                @foreach (BpWizardStep step in Data)
                {
                    <StepperStep Class="@GetStepClass(step)">
                        <Template>
                            <div>
                                @step.Label
                            </div>
                        </Template>
                    </StepperStep>
                }
            </StepperSteps>
        </TelerikStepper>