Unknown exception when generating layout

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First go to View -> Reset Window layout and see if this helps.  If it doesn't then try a reset.  You didn't mention the version you are using so based on Studio 2017 rename this folder (just add _old to the end or something, it's not important what you rename it to) and restart Studio:

c:\Users\[USERNAME]\AppData\Roaming\SDL\SDL Trados Studio\14.0.0.0