Hi Dave,
Sorry for my late reply.
I'd suggest you to try the following:
– use ULS log file and see what SharePoint logs when the error happens (use Microsoft ULS Viewer tool from here http://archive.msdn.microsoft.com/ULSViewer)
– see if the same list item displays ok in the ListForm OOB wp
– try to isolate the issue to the field/value that causes the problem (ie. make the field Rich Text Editor to Plain, remove fields from the list)
– if there is any other web part on the page delete it
– use the Developer Tools (if you run on IE) and see if any js error happens
– use different browsers
Please let me know how that goes.