Thanks for the responses PJ.
I did have some luck switching the neutral and the ground coming in to the switch. Doing this I was able to get the light to turn on when the switched was activated, however if I had a load connected to the switch the breaker would trip. Here is a picture of the spa panel, which I believe is wired correctly.
The NEMA 14-50 receptacle is wired like this, which looks correct
The power cord is this one
Coleman Cable 09046 6-Foot 50-Amp 4-Wire Range Power Cord
and the din modules I used are these
After still getting nowhere. I decided to try something basic, unwiring everything and just trying to power the 110 duplex outlet. The power in to the DIN rail was connect to power on the duplex, neutral in (white wire in) to neutral on the duplex, and ground in (green wire in) to ground on the duplex. Power was switched on and I plugged in a small fan. As soon as I switched the power to the fan on the breaker tripped. I tried switching the neutral and the ground and had the breaker tripped just as it did before. All wires for the 110 were 14 gage. Obviously there is a very basic problem with my setup but I can't figure out what it is.
Could the grounding of the box be causing an issue?