mrbsolution thank you for the referral to those posts.
I've read the threads and if I understand them properly they point to a blocking plugin as the culprit.
I use an IP blocker on my site, the IP's only get added when they try to login and fail. Just to be safe I checked the Google IP's against the list and they are not blocked.
Besides Googlebot works fine when I clear the cache, so the IPs cannot be blocked.
I just de-activated Spamfree WordPress that automatically blocks spam coomments. This was a recent addition, I'll post the results here tomorrow when I check GWMT again.