Error in nls(formula.gompertz, d, starting.values) : singular gradient

I wish I could say, but without a reprex, I have to go all Wittgenstein:

Whereof we cannot speak we must perforce remain silent.

Enough tongue-in-check: really, all that I can do is speculate: Beyond [1:25] are there any NA, NaN, Inf, -Inf or 0 occurrences?