I’ve just come across this thread about SA timeouts:
http://forum.mikrotik.com/t/not-responding-f-k-a-sa-query-timeout/168864/1
This appears to be the problem on my laptop so not the signal issue as such. If I change from WPA2-PSK/WP3-PSK to WPA-PSK/WPA2-PSK, the SA timeout errors stop and my laptop can connect fine. I’m not sure whether this is a problem with RouterOS or the laptop network adapter. Need to do some more reading but my report doesn’t look like a range issue.