After running "install.sh" from https://github.com/psnively/nixops-mac-setup, sourcing "~/.profile", doing "nixops create test/trivial-vbox.nix test/trivial.nix -d test" and "nixops deploy -d test" I get the following error:
error: substituter `/nix/store/3c54dqyd56z91agbjg0041sb3nm5hqv7-nix-1.5.2pre3082_2398417/libexec/nix/substituters/download-from-binary-cache.pl' failed: DBD::SQLite::db do failed: column url is not unique at /nix/store/3c54dqyd56z91agbjg0041sb3nm5hqv7-nix-1.5.2pre3082_2398417/libexec/nix/substituters/download-from-binary-cache.pl line 257, line 1.
I should mention that my fork of nixops-mac-setup merely updates the initial version of Nix installed to 1.5.3. There are no other changes.
This seems like a nix issue. Please create a ticket in the Nix issue tracker.
This was in fact a Nix issue, fixed in commit NixOS/nix@75e12b8.