Hi Richard -
The company standard is currently IE 8. I have reached out to internal company support to ask them that if they get a report of this again to ask the user to try a different browser, I will report back once I hear something.
After I posted the original message I did find an entry indicating a trust between AD Zones had failed, that was around the same date/time as the last series of these which we have forwarded to the network support team.
I have never been denied access I am not a Document Administrator but a plain old can get to everything Administrator.
Thanks for the interest!