Hi Mrangelo,
Did you make sure that you installed Export Content version 2.0.0 on the Joomla 1.5.4 site?
The error message that you are getting is not one that you should get from Export Content and appears to be coming from Joomla core once the data is handed over.
It appears to be the message you get when creating a new article and attempting to leave the content box empty.
Are there any article like that in the section(s)?
Please double check you have the correct versions installed.
You could also, using the edit feature in Export Content check that the article content has been imported correctly.
You could try moving by category or content items to see if you still get the error.
You should think about upgrading from Joomla 1.5.4 to 1.5.6 see here:
http://forum.joomla.org/viewtopic.php?f=8&t=315540
Please post back with your results.
