For NewsGator Inbox, we have created a service release (2.6.7) which needs to be installed to resolve this. Assuming that you have the default “check for updates” alerts set, you should automatically get a message prompting you for the new version. To expedite this, in Outlook: select NewsGator Inbox | Check for Updates. NetNewsWire and Go! were not affected by this.

The problem was caused by these clients referencing the ID’s of posts as signed 32 bit integers (the max of this number is approx 2.1 billion). Today, the number of posts in our system exceeded this amount. While our core platform supported this, several of our clients, as mentioned above, didn’t account for it.