Usually, some Placeholder code is not terminated correctly. Less likely is a corrupt file or system libraries not installed.
Create a new design file and add a Variant and check that.
If still wrong, Run as administrator and retry.
If that works then it can be a duff file.
Usually I remove all Placeholder code and retry.
Next I half the site by deleting pages of a copied design file (never the master) and divide and conquer until something works.
You could upload your design and a TGer could sort it.
Acorn
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