Profibus BF flashing

Basically, in my test setup, I am unable to get any DP slave (specifically, the IM174 interface module) to communicate with the PLC over Profibus.

Setup (see attached PDF):

I have a CPU315-T-2 DP powered by a PS 307 and communicated to via a CP343-1. This is connected via purple Profibus cable to the IM174 using X3 on the CPU. Everything is configured in Hardware Config with exactly the right part numbers. The IM174 is configured to address 6 on the DP(Drive) network. On the IM174, the DIP switch is set to 6 also (pins 4 and 2 are ON). The HW Config compiles and downloads fine and there are no red lights on the CPU, the CP, or the PS.

The problem is that the BF light on the IM174 keeps flashing (indicating a Bus Fault). I have tried switching out the profibus cable as well as switching out the IM174, both had no effect on the problem. I also tried swapping out the IM174 for a ET-200M with IO setup, but the ET-200M had a flashing BF light also.

I think the mystery lies mostly with the CPU. There are a few LEDs on the front, BF1 and BF3, that from the manuals seem like they should be showing a fault when one of the DP slaves is not detected. But they never turn on regardless of whether the slave is even plugged in or not.

I have dug through a fair number of manuals but haven't found anything useful.