I have encountered one so far:
"exception while processing SAML response: authncontext doesn't match requestedauthncontext"
This is from a NS generated email for approval request of electronic bank payments batch.
Still trying to figure out if it's an SAML problem, or a permissions problem... I'm discovering that this particular user has been working outside of our security settings due to one of her roles being set up incorrectly. Has been going on for quite some time (before I got here).