When you receive the error, is it while you're attempting to authenticate? And only for moderators and administrators? If so, what you're running into is likely an IP locking error:
http://lithosphere.lithium.com/t5/support-knowledge-base/IP-Comparison-Failed-Why/ta-p/39222
Basically, for privileged users an additional security check is performed to ensure that the IP address inside the SSO token matches the IP address of the request. If those do not match, the user is not allowed to authenticate.
I would suggest double checking your SSO implementation to ensure that the proper request IP address is being passed through when the token is created. If that's not possible, please file a case via our Case Portal so that our Support team can assist in adjusting your SSO configuration.