I am looking at the effect of permitting standards, rebates, average income, and electricity price on a counties solar capacity (cap). Below is an abbreviated sample of my data.

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input float(cap permit rebate lnincome electric) double houses
1452.547 0 47.61906  10.23742  10.88  578.2945736434108
595.21027 1     5500 10.662493 15.142 14524.418604651162
545.2054 1     5500 10.641537 13.932 14359.302325581395
520.4196 1     5500  10.77956 13.932  7180.232558139534
502.8186 1     5500 10.793516 15.142  7281.782945736434
474.9224 1     5500  10.67165 15.142 1148.8372093023256
398.07135 1     5500 10.635086 13.932 1160.4651162790697
306.4947 0 1.00e-05  10.38539  10.99   4659.68992248062
264.1102 1     5500 10.537601 13.824 14199.612403100775
239.5443 0 1.00e-05 11.136908  10.99   315.891472868217
end

I run the following command

tobit cap permit rebate lnincome electric [aweight = houses], ll robust

I then run the following command:

margins, eydx(rebate) atmeans

I receive the following error:

"could not calculate numerical derivatives -- discontinuous region with missing values encountered"

the following command does work however:

margins, dydx(rebate) atmeans

Would love some ideas about what going on here, thanks so much in advance!