Hi Nanci,
I've exactly the same problem.
The problem is, that nuget automatically adds an trailing slash. So while do the following:
nuget push MyPackage.symbols.nupkg -Source http://MyServer:8624/symbols
nuget adds an trailing slash http://MyServer:8624/symbols/
And while http://MyServer:8624/symbols is working fine, http://MyServer:8624/symbols/ throws an 404 error.
So to use ProGet Symbol Server in a .NET environment would require a behaviour change in ProGet.
It's not hosted in IIS, if that relevant.