I found a pdf with all the screenos messages. I think this one on page 208 is the one to search for.
Message
The NSRP configuration is out of synchronization between the local device and the peer device.
Meaning
The local device to which the administrative session is linked is not synchronized withthepeerdevice (theotherdevice intheNSRP cluster).
Action
Review the NSRP configuration between the two devices and see if they are configured to be peers. Also, check to make sure cables are connected properly and perform a manual synchronization.
https://www.juniper.net/techpubs/software/screenos/screenos6.3.0/630_messages.pdf