Excel VBA Errors For Long Macro Processing?

I have a very long (> 2 hr) macro that sifts through thousands of files and creates a table of contents (more or less). Anyway, the macro will operate just fine when I am also working at the same PC but if I walk away for an hour, Excel will sometimes generate an error (application defined or object defined error). I believe that it has something to do with the PC going idle although it really isn't going idle because I turn off sleep and hibernate while running the macro. Also, there are only two locations where the error seems to occur. See below:

Code:
Dim oApp As ObjectSet oApp = CreateObject("Shell.Application")
Dim files As New Collection
Dim fZip As Variant
For Each fZip In oApp.Namespace(zipFile).items