"Ok, I found the offending line. It was not the pgadmin line. There was a line with a large binary insert."
Not sure if that helps.
It might: there are then some lines like: 2013-10-11 02:44:26.164 BST,"postgres","course_records",19216,"[local]",525740b3.4b10,124887,"idle in transaction",2013-10-11 01:05:07 BST,7/16388,0,LOG,00000,"fastpath function call: ""loread"" (OID 954)",,,,,,,,
I suspect the ""loread"" is the offender.
Thanks to all for the help. I would never have thought to suspect the lines after the one given in the error message.