Negative DNI estimates from DISC model

I am attempting to wrap pvwattsv5 into my own program for estimating solar output over specific historical periods. I have most necessary weather data (GHI, Tdry, Wspd) for input to the module. However, when trying to estimate DNI from GHI using the DISC model, many negative values are being output. The only changes that I have made to the DISC model have been extending equations out to 8760 hours, adding a zero hour to Jan 1, and changing default inputs to inputs from one of my own stations (lat:42.75, long:-73.81, pressure:996). Here are GHI inputs for my first day and the resulting DNI from the DISC:
0, 0.0
0, 0.0
0, 0.0
0, 0.0
0, 0.0
0, 0.0
0, 0.0
0, 0.0
0.2, 0.0
10.9, 0.0
54.5, -15.8
59.5, -9.5
58.8, -7.7
77.9, 1.3
51.1, -15.0
46.4, -23.2
15.9, 0.0
0.1, 0.0
0, 0.0
0, 0.0
0, 0.0
0, 0.0
0, 0.0
0, 0.0

Any insight you can give me into where I have made mistakes would be greatly appreciated. I have also attached the model with GHI data for all 2010. Thanks!