Are you sure the file is named correctly and in that location.

This macro will check

Sub isIt_There()

Dim fso As Object
Dim strpath
strpath = Environ("APPDATA") & "\Microsoft\AddIns\System_File_Location.txt"
Set fso = CreateObject("scripting.filesystemobject")
MsgBox fso.fileexists(strpath)
End Sub
If you are sure it's present and the macro returns False it usually means you do not have permission to access that location. Not likely though.