Pkg.update() error on mac osX: GitError

Couldn’t update julia on mac os X. I am using julia on a ubuntu as well. No issue there. The error message is pasted below:

julia> Pkg.update()
INFO: Updating METADATA…
ERROR: GitError(Code:ENOTFOUND, Class:Repository, Could not find repository from ‘DataFrames’)
Stacktrace:
[1] macro expansion at ./libgit2/error.jl:99 [inlined]
[2] Base.LibGit2.GitRepo(::String) at ./libgit2/repository.jl:10
[3] installed(::Dict{String,Dict{VersionNumber,Base.Pkg.Types.Available}}) at ./pkg/read.jl:211
[4] update(::String, ::Set{String}) at ./pkg/entry.jl:393
[5] (::Base.Pkg.Dir.##4#7{Array{Any,1},Base.Pkg.Entry.#update,Tuple{String,Set{String}}})() at ./pkg/dir.jl:36
[6] cd(::Base.Pkg.Dir.##4#7{Array{Any,1},Base.Pkg.Entry.#update,Tuple{String,Set{String}}}, ::String) at ./file.jl:70
[7] #cd#1(::Array{Any,1}, ::Function, ::Function, ::String, ::Vararg{Any,N} where N) at ./pkg/dir.jl:36
[8] update() at ./pkg/pkg.jl:228

Please help.