The subscriber preview failed to generate. Review the details, correct all issues, and try again. – The specified attribute or custom object field name was not found for this client. Function Call: Lookup(‘MyNTORewards’,MyNTOLevel,’SubscriberKey’,@subscriberkey) Attribute or Field Name: MyNTOLevel
When performing a lookup function in AMPscript, make sure the column names are wrapped in quotes. Solution: change MyNTOLevel to ‘MyNTOLevel’. Reference: Lookup
More to come; this post will be updated on an ongoing basis.