I keep getting these weird errors when trying to compile with Asymptote. I compile with pdflatex, then asymptote, then pdflatex. The error is as stated in the title. For example, when building latexusage.tex (the example asymptote file), it says that on line 91 file 'latexusage-2.tex' not found. The first and last figures are displayed in the produced pdf but the 3D cube is missing. Any ideas what I'm missing?

To install, I used the instructions in this link by Speravir.

It seems the -2.tex is supposed to be the tex file for the second image. The -2.asy and -2.out files are created and in the folder, just not the -2.tex file.

Edit: after trying to make a MWE I'm getting the error C:\Program Files (x86)\Asymptote/three_surface.asy: 906.10: null surface on this code (no error if I delete the label line though):

\documentclass[12pt]{article}
\usepackage{asymptote}
\begin{document}

\begin{asydef}
import three;
usepackage("bm");
texpreamble("\def\V#1{\bm{#1}}");
\end{asydef}

\begin{asy}
draw(unitcube,blue);
label("$V-E+F=2$",(0,1,0.5),3Y,blue+fontsize(17pt));
\end{asy}
\end{document}