My best bet is that you are using Julia v1.0.0 and have using Compat in your startup.jl file. Julia v1.0.0 does not have don't use startup.jl when precompiling, building and testing by fredrikekre · Pull Request #470 · JuliaLang/Pkg.jl · GitHub included. If this is the case you can either (i) upgrade to Julia v1.0.1 (which is recommended anyway) or (ii) start Julia with --startup-file=no and then pkg> build Arpack again.