Content in data mining structure not valid - deployment fails

Hello,

I'm a beginner with SQL 2012 SSDT & SSMS

I get this error message when I try to deploy my project: 

"Error6Error (Data mining): KEY SEQUENCE columns are not supported at the case level. The 'Customer Key' column of the 'TK448 Ch09 Cube Clustering' mining structure contains content that is not valid.00"

I am finding it hard to locate the content that is not valid. I've been trying to find a answer for this problem but can't seem to find anything. How can I locate the content that is not valid and change or delete it so that I can deploy this solution?

Help is much appreciated, thank you!

Best Regards,

Niko