Hi , apologies for the delay.
I saved the calendar list as a template, and deployed this to a test site of mine. Then I linked it up with Quest webpart calendar, which was fine, and worked. This was without the content of the calendar though.
I next saved the calendar list AND it's content, as a template, deployed this on my test site and linked it to the Quest calendar webpart and this was getting the same error.
Obviously there is something in the calendar content that is not supported by the quest webpart, but there are hundreds of entries, how would I go about finding out what exactly this is?