The schema does not prevent duplicate values in the table, as the index is on the parent list ID, the ID (and not the text) of the list value itself and on the language ID. Are you seeing the duplicates when you try to select a value for the attribute?  Or when you view the list itself? Note that since Agile allows multiple languages to be used, each one has a distinct value since whatever the string value is would/could be different in each language.

 When you manually enter the list values using the Java client, it does check whether you are entering any duplicate values. How did you upload the list of values? Are some of them “deleted”, as those would not be visible to users anyway.

I can see duplicate values when I try to add the values in Webclient.
i added the list values manually in java client

So you see duplicate values when you are trying to select a value for the attribute from the drop-down list. Do you see them when you check on the list in the Java client?

 Look at the database, and see if they actually exist. It is possible that some have a trailing blank or something like that, making them not really a duplicate (although it certainly looks like it). In the Java client, find the list parent ID for the attribute. Then execute the following query :
select entryid, ‘<‘ || entryvalue || ‘>’, langid, active from listentry where parentid = <the value you found> order by entryvalue, langid, active;

 This should show you if there really are duplicate values. Note that ACTIVE tells you the status of the value itself – 0 = enabled, 1 = disabled (cannot be selected), 2 = deleted (cannot be seen). You can then set the “duplicate” ones as either disabled or deleted in the Java client (open the list itself, and modify as needed), and things should be good. I would recommend setting them as deleted.

i don’t have any answers, Kev seems to’ve covered almost everything.  i only wonder, in this case of duplicate list entries, if the Apiname on the list entries is different than the values.