Steps
Verify you have Editor or higher permissions on the board
Check that the board file size isn't too large (>50MB)
Ensure all elements are visible (unhide any hidden layers)
Try exporting to a different format (PDF, JPG, PNG, SVG)
Reduce animations or effects and try exporting again
Clear your browser cache and try the export again
Try using a different browser for the export
Check your available disk space for the downloaded file
Notes
Exports work best with modern browsers
Hidden elements won't be included in exports
High resolution exports create larger files
Animations may not export to all formats