Thomas,

     So those messages do not directly indicate a problem, but may still be worth investigating. Is the IP address referenced in the syslog message one of your global address in a 'global' or 'static' config line? If so, it very well may be that a host on the inside is trying to communicate to its own external address:

nat (inside) 1 10.0.0.0 255.0.0.0

global (outside) 1 1.2.3.4

If a host on the inside tries to connect to 1.2.3.4, the packet as it leaves the firewall would look like it is coming from/going to 1.2.3.4 (which would be a land attack).

One way you can track this would be to setup a capture on the inside interface for this traffic:

8.0.4 code and later:

cap inside interfcae inside match ip any host 1.2.3.4

Earlier code:

access-list cap-list permit ip any host 1.2.3.4

cap inside interface inside access-list cap-list

When you see the error pop-up look at the captures:

show capture inside

I hope this helps. If this resolves your issue, please mark this question as resolved.

-Magnus