Is "Invalid Status" showing to all users, or just in the affected agent's client?
If all users
except the affected agent, then perhaps that agent is changing their status to something they have access to but others don't (maybe a member of one more workgroup or role).
Or, perhaps there is a network communication error somehow happening randomly...
I think the SessionManager log might show the status change messages, probably in conjunction with the ClientServices log - I'd check those to see if you can track what status was trying to be set.
Also check the InteractionClient log on the agent's desktop to see if you can find info on the status change...I can't remember if that has the info. Might have to turn up tracing on the agent's machine to see it.