You need to find the object in error. Check the .OUT and .EEX files/datasets for any messages. When you find the object the extract fell over on first of all check to see if it is a valid Natural object. If it is invalid then remove it from the library that NEE is processing as it cannot be a production object and re-run extract.
If it is a valid Natural Object then you need to raise a support request with your local support centre giving them the error, the object in question and any related data areas/copycodes/DDMs rto recreate the error. You will need to tell them platform, version of Nat/Nee etc.You could then remove the offending object from the processing and re-run extract. The valid object could then be re-extracted later once the parser has been fixed to handle the exception.