I am running Julia v.0.5. and Graphs v. 0.6 on OS El capitan. The full error I get is :
inlined code] from ./strings/io.jl:73
in _jl_spawn(::ASCIIString, ::Array{ByteString,1}, ::Ptr{Void}, ::Base.Process, ::Base.PipeEndpoint, ::Base.DevNullStream, ::Base.TTY) at ./process.jl:332
in setup_stdio(::Base.##170#171{Cmd}, ::Tuple{Pipe,Base.DevNullStream,Base.TTY}) at ./process.jl:485
in #spawn#169(::Nullable{Base.ProcessChain}, ::Any, ::Cmd, ::Tuple{Pipe,Base.DevNullStream,Base.TTY}, ::Bool, ::Bool) at ./process.jl:484
[inlined code] from ./boot.jl:331
in open(::Cmd, ::ASCIIString, ::Base.DevNullStream) at ./process.jl:551
[inlined code] from ./process.jl:543
in plot(::Graphs.GenericGraph{Int64,Graphs.Edge{Int64},UnitRange{Int64},Array{Graphs.Edge{Int64},1},Array{Array{Graphs.Edge{Int64},1},1}}) at /Users/mac/.julia/v0.5/Graphs/src/dot.jl:91
in eval(::Module, ::Any) at ./boot.jl:267