Circular Dependency Error

Hi, 

I have three tables: 

A) clarity allocations

B) clarity available 

C) cdl resources monthly 

A and B are joined on "pmfkey" with C 

I want to create:

a) a column in table C, which will bring the "Future Alloc Col" from table A and

b) a column in table C, which will bring the "FutureAvailable Col" from table B

I have done a) succuessfully using the following calculation

Future Allocations Column = CALCULATE(SUM('CLARITY ALLOCATIONS'[Future Alloc Col]),USERELATIONSHIP('CLARITY ALLOCATIONS'[PMFKEY],'cdl resources monthly'[PMF Key]))

However, trying to use exactly the same logic in order to achieve b), fails

I have gone through the Circular Dependencies threads, which are not very easy to understand to be honest, but I have deleted numerous relationships among my tables in order to keep it as simple as possible and avoid this type of errors. Even if there is no t a solution, can somebody explain why I can bring the column from table A to table C and I can't do the same from table B to C?

It is vital to have all these columns in table C, because this tabel drives the visualizatio as it is the table with Unique pmfkeys on which I can create relationships to.