This is due to several security features that Gmail has implemented. If any constituent flags a Convio/Blackbaud email from your org as spam, Gmail will display that flag on all Convio/Blackbaud emails from your org throughout the system. This error will go away after some time if no other emails from your organization are flagged as spam. Our Service Delivery Operations team is continually working with all email clients to ensure that our emails are not marked as spam. 

Since this is dependent upon how constituents react to email, this status can change regularly and seem somewhat random.