Its very difficult to say what the problem is without seeing the data or a packaged workbook (.twbx file). Are you able to share your packaged workbook? Thanks!
Here is one link that may provide a bit of help: http://kb.tableausoftware.com/articles/knowledgebase/removing-duplicated-data-after-join
thanks for the quick response. Blending does solve the issue itself but it would also mean that I would have to redo the complete workbook. However as since that seem to be the only way possible, I ll guess I have to do it .
Unfortunately the data is of confidential manner and thus can't really post it.
There are usually other options, but they may require more advanced calculations to implement. Again, its difficult to say without seeing any data. Data blending is often a good option in these scenarios, but blending has its own limitations as well as advantages. Best of luck on whatever you do decide!