Since v.0.7.0-beta, build GR or build Arpack (and some more packages that I cannot recall) fails whenever my startup.jl contains using Statistics (you can swap that for any other package name, I think). Example of the result:
> build Arpack
Building Arpack → `C:\Users\Me\.julia\packages\Arpack\uM2QD\deps\build.log`
┌ Error: Error building `Arpack`:
│ ERROR: LoadError: ArgumentError: Package Statistics not found in current path:
│ - Run `Pkg.add("Statistics")` to install the Statistics package.
│
│ Stacktrace:
│ [1] require(::Module, ::Symbol) at .\loading.jl:819
│ [2] top-level scope at C:\Users\Me\.julia\config\startup.jl:10
│ [3] include at .\boot.jl:317 [inlined]
│ [4] include_relative(::Module, ::String) at .\loading.jl:1040
│ [5] include at .\sysimg.jl:29 [inlined]
│ [6] include_ifexists at .\client.jl:201 [inlined]
│ [7] load_julia_startup() at .\client.jl:298
│ [8] exec_options(::Base.JLOptions) at .\logging.jl:312
│ [9] _start() at .\client.jl:432
│ in expression starting at C:\Users\Me\.julia\config\startup.jl:8
This solution is easy (comment out the offending line, before updating), but will not be convenient for new users.