You haven't provide any code, but such problem could occur if you are using DestroyOnClose set to true for the RadWindowManager. If this is your scenario, try setting it to false and see how your app will behave.
When this property is set to true, RadWindow’s object will be destroyed once the window is closed. This, however, means that you will not be able to open that same RadWindow again until the whole page is reloaded. In such scenario, it will be best to either set all needed properties (width, height, modality, etc.) to the RadWindowManager or as an alternative – to use the client-side API
and set them when opening the RadWindow.
If this is not your case, please open a support ticket and send us a sample project that reproduces the problem. This blog post
will help you isolate the problem in a separate project.
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