We too are having problems logging on with our 3 macs - it was all working fine until recently but now the login process stops before completing yet nothing has changed here.  Our Windows computers work fine which suggests this is not a network issue here.  We have checked against the system requirements for Mac OS and browser (Chrome/Safari & Firefox) - all fine but unable to login.  We have done the usual clear cache/history but no use.

Did you get anywhere with your mac being unable to login because QB support don't seem to be able or willing to investigate, the two staff I spoke to lacked any skills in troubleshooting.