I got this error a couple of times too. At the time, I had once instance of client 54 running and one instance of client 57 running on the same machine (because 54 worked with acroforms but not Rx faxing, and 57 worked with Rx faxing but not acroforms... that's since been fixed). When I got the read-only mode error message, I just closed out all the synapse clients (in Windows taskmanager, took 'em all down), and relaunched and the error went away. I haven't been able to recreate it since.
I got the read only when trying to add a result. Rebooting Synapse always solves this ... until the next time.
That's probably why I get that. Can that be fixed ? or would that be a requirement: must shut down clients daily.