generate.nix hash mismatch

nix build -f generate.nix --argstr format virtualbox --argstr configuration ./configuration.nix config.system.build
builder for '/nix/store/mxfj0xfi6fsfxr3k691f9pv41v8f2xmx-nixos-ova-20.09pre-git-x86_64-linux.drv' failed with exit code 1; last 10 log lines:
  copying path '/nix/store/0y4fr7ri13y8ixpcyg56ldnas2hwjhij-nss-3.52' to 'local'...
  copying path '/nix/store/qvy7i2yq8b8i3rap71ryismn8r30lmxr-perl5.30.2-DBD-SQLite-1.64' to 'local'...
  copying path '/nix/store/2xqh8234jmxrlh4r3xhw4ihg87qzjxjx-polkit-0.116-bin' to 'local'...
  copying path '/nix/store/4gwhvfaqgj84cq3mmg8ca6wxvnwgwggs-command-not-found' to 'local'...
  copying path '/nix/store/38kz3j1a87cq5y59k5w7k9yk4cqgc5b2-python-2.7.18' to 'local'...
  hash mismatch importing path '/nix/store/38kz3j1a87cq5y59k5w7k9yk4cqgc5b2-python-2.7.18';
    wanted: sha256:0m28zrci46ss7nm3v98v3w0xd0z21znbggsqbzy2smkaqcki2m9d
    got:    sha256:17il50r6s2jl23c5dpccs0h61c2q3dywhgwynmk16pnsdd1m89sl
  copying path '/nix/store/2dcsn57cgaxs92ha5swihrab0g3l2h6g-python3-3.7.7' to 'local'...
  error: path '/nix/store/x57i1nkjswb2vgbi2lnqdky7rh7bsa84-nixos-system-nixos-20.09pre-git' does not exist and cannot be created
[0 built (1 failed)]
error: build of '/nix/store/mxfj0xfi6fsfxr3k691f9pv41v8f2xmx-nixos-ova-20.09pre-git-x86_64-linux.drv' failed