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This may correct the problem if the layer was off or frozen. Double check that the layer is ON and THAWED.
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Check the properties and note which layer the viewport is on.If other viewports are in the layout tab, remove them from the selection set by holding down the Shift key and selecting each visible viewport, leaving just the invisible viewport selected.On the Quick Select dialog box, set the Object type to Viewport and click OK.From the Properties palette, select the Quick Select button on the top right.Go to the layout tab that contains the problem viewport.In the Layer Properties Manager, make sure the layer that contains the viewport geometry is not turned off or frozen.Solution:Make sure the layer has not been turned off or frozen:
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