These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 1.55 s (backtrack: 0/20).

[ebuild  N     ] acct-group/vlock-0-r2::gentoo  0 KiB
[ebuild  N     ] app-misc/vlock-2.2.3-r2::gentoo  USE="pam (-selinux) -test" 54 KiB
[blocks B      ] sys-apps/kbd[pam] ("sys-apps/kbd[pam]" is soft blocking app-misc/vlock-2.2.3-r2)
[blocks B      ] app-misc/vlock ("app-misc/vlock" is soft blocking sys-apps/kbd-2.9.0-r1)

Total: 2 packages (2 new), Size of downloads: 54 KiB
Conflict: 2 blocks (2 unsatisfied)

 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

  (sys-apps/kbd-2.9.0-r1:0/0::gentoo, installed) pulled in by
    sys-apps/kbd required by @system 

  (app-misc/vlock-2.2.3-r2:0/0::gentoo, ebuild scheduled for merge) pulled in by
    =app-misc/vlock-2.2.3-r2


For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):

https://wiki.gentoo.org/wiki/Handbook:X86/Working/Portage#Blocked_packages