Error with Pkg.add() (with packages using Documenter?)

On Julia v0.5.0, Windows, I get the following error when trying to Pkg.add("AxisArrays").
Similar error when trying to Pkg.add("Compose").
I suspect both of these packages use Documenter.

julia> Pkg.add("AxisArrays")
INFO: Installing AxisArrays v0.0.3
ERROR: GitError(Code:ERROR, Class:OS, Could not open 'C:/Users/plowman/.julia/v0.5/AxisArrays/docs/.documenter.enc' for writing: Access is denied.
)
 in macro expansion at .\libgit2\error.jl:99 [inlined]
 in clone(::String, ::String, ::Base.LibGit2.CloneOptions) at .\libgit2\repository.jl:191
 in #clone#109(::String, ::Bool, ::Ptr{Void}, ::Nullable{Base.LibGit2.AbstractCredentials}, ::Function, ::String, ::String) at .\libgit2\libgit2.jl:327
 in install(::String, ::String) at .\pkg\write.jl:40
 in resolve(::Dict{String,Base.Pkg.Types.VersionSet}, ::Dict{String,Dict{VersionNumber,Base.Pkg.Types.Available}}, ::Dict{String,Tuple{VersionNumber,Bool}}, ::D
ict{String,Base.Pkg.Types.Fixed}, ::Dict{String,VersionNumber}, ::Set{String}) at .\pkg\entry.jl:530
 in resolve(::Dict{String,Base.Pkg.Types.VersionSet}, ::Dict{String,Dict{VersionNumber,Base.Pkg.Types.Available}}, ::Dict{String,Tuple{VersionNumber,Bool}}, ::D
ict{String,Base.Pkg.Types.Fixed}) at .\pkg\entry.jl:476
 in edit(::Function, ::String, ::Base.Pkg.Types.VersionSet, ::Vararg{Base.Pkg.Types.VersionSet,N}) at .\pkg\entry.jl:30
 in (::Base.Pkg.Entry.##2#5{String,Base.Pkg.Types.VersionSet})() at .\task.jl:360
 in sync_end() at .\task.jl:311
 in macro expansion at .\task.jl:327 [inlined]
 in add(::String, ::Base.Pkg.Types.VersionSet) at .\pkg\entry.jl:51
 in (::Base.Pkg.Dir.##2#3{Array{Any,1},Base.Pkg.Entry.#add,Tuple{String}})() at .\pkg\dir.jl:31
 in cd(::Base.Pkg.Dir.##2#3{Array{Any,1},Base.Pkg.Entry.#add,Tuple{String}}, ::String) at .\file.jl:48
 in #cd#1(::Array{Any,1}, ::Function, ::Function, ::String, ::Vararg{Any,N}) at .\pkg\dir.jl:31
 in add(::String) at .\pkg\pkg.jl:100

Not sure if I need Documenter installed, but I get this error when trying to install:

julia> Pkg.add("Documenter")
INFO: Updating cache of Documenter...
INFO: Installing DocStringExtensions v0.3.1
ERROR: GitError(Code:ENOTFOUND, Class:Repository, Could not find repository from 'DocStringExtensions')
 in Base.LibGit2.GitRepo(::String) at .\libgit2\repository.jl:11
 in install(::String, ::String) at .\pkg\write.jl:38
 in resolve(::Dict{String,Base.Pkg.Types.VersionSet}, ::Dict{String,Dict{VersionNumber,Base.Pkg.Types.Available}}, ::Dict{String,Tuple{VersionNumber,Bool}}, ::D
ict{String,Base.Pkg.Types.Fixed}, ::Dict{String,VersionNumber}, ::Set{String}) at .\pkg\entry.jl:530
 in resolve(::Dict{String,Base.Pkg.Types.VersionSet}, ::Dict{String,Dict{VersionNumber,Base.Pkg.Types.Available}}, ::Dict{String,Tuple{VersionNumber,Bool}}, ::D
ict{String,Base.Pkg.Types.Fixed}) at .\pkg\entry.jl:476
 in edit(::Function, ::String, ::Base.Pkg.Types.VersionSet, ::Vararg{Base.Pkg.Types.VersionSet,N}) at .\pkg\entry.jl:30
 in (::Base.Pkg.Entry.##2#5{String,Base.Pkg.Types.VersionSet})() at .\task.jl:360
 in sync_end() at .\task.jl:311
 in macro expansion at .\task.jl:327 [inlined]
 in add(::String, ::Base.Pkg.Types.VersionSet) at .\pkg\entry.jl:51
 in (::Base.Pkg.Dir.##2#3{Array{Any,1},Base.Pkg.Entry.#add,Tuple{String}})() at .\pkg\dir.jl:31
 in cd(::Base.Pkg.Dir.##2#3{Array{Any,1},Base.Pkg.Entry.#add,Tuple{String}}, ::String) at .\file.jl:48
 in #cd#1(::Array{Any,1}, ::Function, ::Function, ::String, ::Vararg{Any,N}) at .\pkg\dir.jl:31
 in add(::String) at .\pkg\pkg.jl:100

I was able to install Compose and Documenter without issues on Windows 10. Packages using Documenter shouldn’t know anything about Documenter until you actually try to build the docs, so I don’t think this is related to Documenter. It looks like git/libgit is somehow problematic.

Is it a clean Julia installation from the 0.5.0 installer? Perhaps someone more knowledgeable will pass by but it might be worth posting it to the Julia issue tracker.

I can successfully install Compose, Images (which installs AxisArrays) and Documenter from my home PC running Windows 10.

The errors shown above are from my work PC running Windows 7 through corporate proxy.
So as you say, maybe error is something to do with libgit2.