Hello,
n
Can you please let me know your QA and SharePoint version? Also please attach the web part and lists templates (with or without the data). Also please check the internal field names of both lists, they have to match.To find the field internal name take a look here: https://www.nothingbutsharepoint.com/sites/devwiki/SP2007Dev/Pages/Getting%20the%20Field%20by%20the%20Internal%20Name.aspx
n
Thanks,
n