Accessing columns in joined table

[AK-Ing]

I've got two tables "A1J01" and "A3J18". Out of the table "Abfrage1" i would access the column "Wirkleistung" in "A1J01" and "A3J18" to calculate a sum. The DAX formula in "Abfrage1" to create a new column should be:

"=A1J01[Wirkleistung]+A3J18[Wirkleistung]"

but it doesn't work. There is an error reported (origin in german):

"Ein einzelner Wert für Spalte 'Wirkleistung' kann in Tabelle 'A1J01' nicht ermittelt werden. Dies kann vorkommen, wenn eine Measureformel auf eine Spalte verweist, die viele Werte enthält, ohne eine Aggregation wie 'min', 'max', 'count' oder 'sum' anzugeben, um ein einzelnes Ergebnis zu erhalten." 

translated:

"A single value for column 'Active Power' cannot be determined in table 'A1J01'. This can happen when a measure formula references a column that contains many values without specifying an aggregation such as 'min', 'max', 'count', or 'sum' to get a single result."

The formula is for column not measure. Amazingly a measure formula like "Measure 1:=sum(A1J01[Wirkleistung])" works and delivers while typing a preselection "A1J01[Wirkleistung]" in the calculation line.

All tables are connected/related over the time column.

Does anyone have an idea whats going wrong?

[AK-Ing · Accepted solution]

... in the meantime i've found the problem. It's my fault ...

The direction of the relationsship was wrong, therefore no related junction was possible.
Changing the direction of the relation and using DAX-formula as "=RELATED(A1J01[Wirkleistung])" worked.

[FreemanZ]

hi @AK-Ing 

could you elaborate what does this mean: All tables are connected/related over the time column?

[AK-Ing]

Hi @FreemanZ

there is a relationsship between the datetime columns of each table to the primary table "Abfrage1" (primary key). Normaly the calculation between columns out of different tables/queries works fine in pover pivot. But this time if i try to reach the columns in table "A1J01" or "A3J18" i get the above named error.

I solved the problem temporaly by joining the tables "A1J01" and "A3J18" (left outer) with "Abfrage1".

But in the end it is fine to know why this error occurs ...