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I would suggest that you review the following solution from the ColorQube 8700 Support website.
Fault Code 391.535.00, 091-535, 391.535, 91-535:
If that does not resolve your issue you may consider contacting our specific product support experts for customers in the USA & Canada at the following link: Fast Track to the Expert
Chat is also be available from the Contact tab on the support site (link above) for this product.