Can'r create a Direct Active Relationship

Hi

I have a number of different data tables [DT1:DT7] which have a relationship to a single employee table [Emp} so that I can pick an employee from [Emp} and it will filter all seven tables - this is working fine

I now have an 8th data table that I also want to create a relationship to [Emp] but it is saying I cannot as would introduce ambiguity between Emp & DT3

I can't see why this works on the other DTs but not DT8

This explains the relationships that are already working:

DT1 Employee_SID Relates to Emp EmpID

DT2 UserID Relates to Emp EmpID

DT3 Employee_SID Relates to Emp EmpID

DT4 OwnerID Relates to Emp EmpID

DT5 Emp_ID Relates to Emp EmpID

DT6 Owned_BYID Relates to Emp EmpID

DT7 ChngdByID Relates to Emp EmpID

And the one that is now causing the issue

DT8 CreatedBYID Relates to Emp EmpID

Thanks in advance for any advice