DateTime format exception after upgrade to 6.4

I've just run the automatic upgrade to 6.4.0.56 (from 5.something I think). We have 2 licensed servers and both went through the upgrade process without any errors, but one is now reporting a problem (the other one is fine)

System.FormatException: The DateTime represented by the string is not supported in calendar System.Globalization.GregorianCalendar.
at System.DateTimeParse.ParseExact(String s, String format, DateTimeFormatInfo dtfi, DateTimeStyles style)
at RedGate.SQLBackup.Engine.SQLMarshaller.MarshallToDateTime(Int32 date, Int32 time)
at RedGate.SQLBackup.Engine.Schedule..ctor(Server server, Job job, SqlDataReader dataReader)
at p.a(Server , Job )
at RedGate.SQLBackup.Engine.Job.a(SqlDataReader )
at RedGate.SQLBackup.Engine.Job..ctor(Server server, SqlDataReader dataReader)
at i.a(Server , SqlDataReader )
at p.a(Server )
at RedGate.SQLBackup.Engine.Server.RefreshJobInformation()

Any ideas what the problem is? If someone can give me a hint on which tables to look in I can start searching for any strangely formatted dates.

Many thanks,
Paul.