Processing Dimension completed but error occurs
If you take a look at your dimension table and run a query like the following:

Select count(suspect_column) as count_suspect_column, suspect_column
from Dimension_Date
GROUP BY suspect_Column
HAVING COUNT(suspect_column) &gt; 1


It is likely that there is a duplicate value causing the process to fail. These values in that column need to be unique for the process to work. Also worth noting is that SSAS treats nulls as empty strings according to this excellent article:
https://www.sqlservercentral.com/articles/ssas-error-duplicate-attribute-key-found-when-processing