Join functionality - how analytically find the error?

Hello, I use a data model that has been working well for a long time. Data records are added at regular intervals (weekly). Now I got in a few components the following error message: No common parent between table could be found - please check your schema. The Tables [Table1.DATA] and [Table2.DATA] are connected, but have no common parent table. Join path [Table1]N 1![CASES]!1>N[Table2]. For more information on the join path, search for Join functionality in PQL documentation. I already checked the fields that are linked in the data model. [Table1.Data].[Field] = MULTIPLE keys [CASE].[key] = UNIQUE key [Table2.Data].[Field] = UNIQUE key I checked this with the following code: SELECT Field, COUNT(Field) AS Anzahl FROM Table2 GROUP BY Field HAVING (COUNT(Field)>1); Does anyone have an idea how the analysis of the error can be advanced here? Is it really only due to one of the tables described in the error or is it possibly due to a different table in the data model? Why is the table described with an N in the error message, even though the content of the connected field is unique? many thx