Unexpected error when installing any package

I recently installed Net Framwork 4.8 on my Windows 7 pack 1. After that when installing any package I get this error :

(@v1.5) pkg> add GitHub #For example
Updating registry at myhome\.julia\registries\General

ERROR: GitError(Code:ENOTFOUND, Class:Odb, object not found - no match for id (ffd07f4a034336b4e61400a015a6d78fd654bcc0))

Stacktrace:
[1] macro expansion at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\LibGit2\src\error.jl:106 [inlined]
[2] LibGit2.GitTree(::LibGit2.GitRepo, ::String) at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\LibGit2\src\repository.jl:142
[3] isdiff(::LibGit2.GitRepo, ::String, ::String; cached::Bool) at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\LibGit2\src\LibGit2.jl:155
[4] #isdirty#112 at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\LibGit2\src\LibGit2.jl:132 [inlined]
[5] isdirty at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\LibGit2\src\LibGit2.jl:132 [inlined] (repeats 2 times)
[6] update_registries(::Pkg.Types.Context, ::Array{Pkg.Types.RegistrySpec,1}; force::Bool) at C:\buildbot\worker\package_win64\build\usr\share\julia

\stdlib\v1.5\Pkg\src\Types.jl:1
145
[7] update_registries at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\Pkg\src\Types.jl:1106 [inlined] (repeats 2 times)
[8] add(::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1}; preserve::Pkg.Types.PreserveLevel, platform::Pkg.BinaryPlatforms.Windows,

kwargs::Base.Iterators.Pairs{Union{},Union
{},Tuple{},NamedTuple{(),Tuple{}}}) at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\Pkg\src\API.jl:172
[9] add(::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1}) at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\Pkg\src\API.jl:139
[10] #add#21 at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\Pkg\src\API.jl:67 [inlined]
[11] add(::Array{Pkg.Types.PackageSpec,1}) at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\Pkg\src\API.jl:67
[12] do_cmd!(::Pkg.REPLMode.Command, ::REPL.LineEditREPL) at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\Pkg\src\REPLMode

\REPLMode.jl:404
[13] do_cmd(::REPL.LineEditREPL, ::String; do_rethrow::Bool) at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\Pkg\src\REPLMode
\REPLMode.jl:382
[14] do_cmd at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\Pkg\src\REPLMode\REPLMode.jl:377 [inlined]
[15] (::Pkg.REPLMode.var"#24#27"{REPL.LineEditREPL,REPL.LineEdit.Prompt})(::REPL.LineEdit.MIState, ::Base.GenericIOBuffer{Array{UInt8,1}}, ::Bool) at
C:\buildbot\worker\package_wi
n64\build\usr\share\julia\stdlib\v1.5\Pkg\src\REPLMode\REPLMode.jl:546
[16] #invokelatest#1 at .\essentials.jl:710 [inlined]
[17] invokelatest at .\essentials.jl:709 [inlined]
[18] run_interface(::REPL.Terminals.TextTerminal, ::REPL.LineEdit.ModalInterface, ::REPL.LineEdit.MIState) at C:\buildbot\worker\package_win64\build
\usr\share\julia\stdlib\v1.5\RE
PL\src\LineEdit.jl:2355
[19] run_frontend(::REPL.LineEditREPL, ::REPL.REPLBackendRef) at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\REPL\src
\REPL.jl:1144
[20] (::REPL.var"#38#42"{REPL.LineEditREPL,REPL.REPLBackendRef})() at .\task.jl:356

**Can someone tell me where is the problem.** **Thanks for any contribution**.