Jupgrade joomla 1.5 - 1.7 export import question

Hi all, have upgraded joomla site from 1.5 -1.7 using jupgrade re-installed uddeim, followed some instructions found here to export from old table into new table, however whenever I try to do this I get the below error, can anyone with some expertise shed any light on this,

Cheers
Chris

#1062 - Duplicate entry '21' for key 'PRIMARY'

Have you tried to import the data twice?
Were all tables empty when you imported the data?

Hi Mate thanks for the fast reply, yes the new j25_uddeim table was empty, the only message was the welcome to uddeim message, which I deleted, I went back to the old site and upgraded to 2.8 thinking that may have something to do with it re-exported and tried importing but same message, very strange considering it is saying there is a duplicate but the tables are empty, if you can give me any other ideas to try would be greatly appreciated.

Cheers
Chris.