OK. Unchecked all of the auditing for that document type. Restarted Trim and it looks like preview is now working.
I then enabled the auditing on that document type again and restarted Trim. The preview is still working. Just a note that not all of the auditing was enabled on that record type, and when I re-enabled the auditing I only enabled it on what was enabled before.
It looks like this has caused another issue. By using the Trim 7.1 client to change the record type audit events has caused the Trim form for this record type to go all screwy on anyone running Trim version 6.2.4... AAAAAAARGH!!!
I am looking at how to fix this now...it's urgent!!!