Not possible to Assign a Source of Supply

I americium getting a Warning connection no: ME123, " Supplying and receiving plants identical (please check)" While I americium trying to delegate root of supply, successful Source of proviso Tab.

This is lone a informing connection yet it inactive doesn't delegate the root of supply. 

I maintained

1. Source list

2. Info grounds with the aforesaid vendor and Material combination.

3. I person ticked the root database nether purchasing tab successful the maestro data.

The proviso works and works successful our lawsuit is the same, but I request it to let maine to delegate the root of supply. 

Please explicate maine the problem

Thanks successful Advance