This error happens rarely in virt-inspector: download: guestfs_download reply failed, see earlier error messages at [...] when downloading the /boot/initrd*.img. There are no 'earlier error messages'. Possibly an instance of bug 501888 (although there is no 'internal error: reply callback called twice' which we would expect to see). Also possible that this is a bug or untested corner in the Perl bindings.
This changeset should ease the problem although it is only a workaround: http://git.et.redhat.com/?p=libguestfs.git;a=commitdiff;h=4dff42aa13dd726fb6b02843d0f4db4b4b330fe3
We think the following patch should fix this error comprehensively: http://git.et.redhat.com/?p=libguestfs.git;a=commitdiff;h=0a0d743ba80e33e676084f2a254c63d4188857b0
libguestfs-1.0.70-1.fc11 has been submitted as an update for Fedora 11. http://admin.fedoraproject.org/updates/libguestfs-1.0.70-1.fc11
libguestfs-1.0.70-1.el5 has been submitted as an update for Fedora EPEL 5. http://admin.fedoraproject.org/updates/libguestfs-1.0.70-1.el5
libguestfs-1.0.70-1.fc11 has been pushed to the Fedora 11 stable repository. If problems still persist, please make note of it in this bug report.
As noted in comment 2, the communications code was extensively rewritten which should obsolete this bug.