Window is maximized but error message comes up that Window is not maximized

Hello I have Problem in running my Telerik Test.

During selecting an Item from a Combobox it comes up a message that said the actual Window is not maximized. But the Window ist maximized. The Error did not comes in everytime only sometimes. But i am worry about it.
The error message is:


'Fail' : 6. Select by text 'Titel' in MetadataComboBoxCombobox
------------------------------------------------------------
Failure Information:
~~~~~~~~~~~~~~~
Point (394, 1015) outside bounds of browser window: (0, 105, 1280, 879)
You might need to maxmize the browser while running this test. Try adding the following code in a coded step: ActiveBrowser.Window.Maximize();
InnerException:
System.InvalidOperationException: Point (394, 1015) outside bounds of browser window: (0, 105, 1280, 879)
You might need to maxmize the browser while running this test. Try adding the following code in a coded step: ActiveBrowser.Window.Maximize();
at ArtOfTest.WebAii.Silverlight.SilverlightApp.ValidateMouseLocation(Point point)
at ArtOfTest.WebAii.Silverlight.UserInteraction.Click(MouseClickType clickType, Point offsetPoint, OffsetReference reference)
at ArtOfTest.WebAii.Silverlight.UserInteraction.Click(MouseClickType clickType)
at ArtOfTest.WebAii.Silverlight.UI.ComboBox.SelectItemByText(Boolean simulateRealUser, String text)
at ArtOfTest.WebAii.Silverlight.UI.ComboBox.SelectItemByText(Boolean simulateRealUser, String text, Boolean openDropDownBeforeSelection)
at ArtOfTest.WebAii.Design.IntrinsicTranslators.Silverlight.Descriptors.ComboBoxSelectItemActionDescriptor.Execute(IApplication hostApp)
at ArtOfTest.WebAii.Design.Extensibility.XamlActionDescriptor.Execute(IAutomationHost autoHost)
at ArtOfTest.WebAii.Design.Execution.ExecutionEngine.ExecuteStep(Int32 order)                                                                  

Please help me. Christian