It seems that upstream modified VirtualBox-4.1.6.tar.bz2 and as a result its checksum and size differ from what is declared in the manifest file.
Oh dear... why can't they just increase the version number?
+*virtualbox-4.1.6-r1 (06 Nov 2011)
+ 06 Nov 2011; Lars Wendler <firstname.lastname@example.org> -virtualbox-4.1.6.ebuild,
+ Revision bump because upstream re-released tarballs (bug #389773).
All other affected virtualbox packages were updated as well.
Thanks for reporting.