Record Track Monitor Cuts Out

My Gear
Intel Quad Core
8 gig ram
M-Audio Pro-Fire 610
KRK Rokit6 Monitors
Ardour Mixbus 2.0.7
(built from Ardour svn 11700)
JACK Audio Connection Kit - Qt GUI Interface - of course

My Problem

Whilst multi-tracking I open up 8 tracks for recording. I record 4 tracks of guitar with no monitoring problems (Mixbus does monitoring) then when I try to record on track 5 it’s montitoring cuts out. I can still hear the other 4 tracks. I’ve checked the channel strips and can see no difference in the set-up. I’ve also disconnected inputs from tracks 1 to 4 thinking there was maybe a conflict. Nothing I do works. I know I’m more than likely missing the obvious but need help in pointing me in the right direction.
I notice I get the following message when opening up the saved project:

ERROR]: AudioSetup value for interface is missing data
[ERROR]: AudioSetup value for inputdevice is missing data
[ERROR]: AudioSetup value for outputdevice is missing data
[INFO]: Loading session /home/ian/Crazed With Effort using snapshot Crazed With Effort (1)
Loading history from ‘/home/ian/Crazed With Effort/Crazed With Effort.history’.

Question 1: Can anyone advise me what I’m doing wrong???

Question 2: I’m also hoping someone can advise why I can’t get the Profire to do the monitoring?

Thanks peeps.