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Do you have any linked files in the project? If you select the level does it appear to be in a link? You should be able to TAB select the level through the link if this is the case [and hide if needed].
Also if you can select the level in an elevation view, can you right-click and either hide the level in view or delete the level from the project?
Additionally, can you double-click on the level to activate the associated view? Or was it a copy of another level for example [where the level appears black instead of the default blue]?
Feel free to attach a screen capture if this does not cover the issue...