Errors about "eval()'d code" stem from plugins or themes (long story short: Q2A rewrites theme code and layer plugins on the fly so they can all work together).
So try disabling plugins one by one until the warning goes away and that will be the culprit. After that look for uses of the count() function, probably something like count(@$var...)
If you're unable to debug it yourself, report it to the plugin developer.