Dataflow query validation error with referenced tables

Hi everyone,

I need some help with a dataflow I am currently working on.

Table A pulls a list of Excel files from a SharePoint folder.

Table B references to Table A and loads a named range from each Excel file and combines them to a single table.

Table C also references to Table A and loads another named range from each Excel file and combines them to a single table. 

Table D combines Table B and Table C to have a single output table.

Now I would like to add two referenced tables (to Table B and Table D) but once I have created another referenced table, I get an unexpected error when validating my query:

Would be great if you can help me fixing this issue! 🙂

Here is the diagram overview of my dataflow: