Since a bunch of days WMT reports "access denied" on more and more domains and pages. Plenty 522 and much more 403.
Webhosting says, that they ain't blocking Google IPs and all pages perform well.
Running exactly the same .htaccess and robots.txt sinces ages on all sites and only since June 7 the crawling has stopped.
Inside WMT robots.txt is declared as missing, but when clicking on "see live version" it shows up right away.
Webhost recommends to contact Google, but who would expect a reply?