Well, the most bothersome one of these counters is the CRC errors. This generally indicates a physical layer issue. How are these interfaces physically connected? x-over, switch, etc..? Did you try swapping out the cable and seeing what this did. The syslog message you indicated in the original post means that the hello packets that the two PIX's exchange with one another were not received for an interval that is 3 X your hello send interval (15 secs by default I think). We then put an interface in testing rather than fail the whole box to make sure there really is a problem. You interface is passing the test which is keeping the failover from occuring. What kind of traffic do you have a on int5? If this is your lan failover link, any chance you had issued a 'wr mem' just before the syslogs?
So, in summary, the syslogs are not necessarily a problem but they should be investigated. But we probably need a bit more info to help.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...