I recently had some issues with my virtual box setup (ran out of physical disk space, bummer, really hoses up the kernel booting :( )
So. .  After some trial error, here's what I got:
HOST:     MAC OS X 10.10.5
VBOX:     4.3.32 r103442
GUEST:   FedoraCore 22 - LXDE Edition

Install, etc. went OK (though did take a couple of tries). . . 
When I try to in VBOX to insert the GuesAdditions (needed to build for shared folder support and bigger screen), the 4.0.4 kernel selected in the boot screen will NOT mount this CD image (located in the virtual box application on OS X).  
I get a "Status 32:  Mount: unknown file type iso9660".

When I boot into the 4.2.3 kernel (save VM version/program) - things worked "better" - with the exception that it failed to build the X-11 support, so my window won't go full screen (27" monitor) - but the Shared Folders are there, which is more important to me.

Googling didn't shed any light on this issue, and it seems to be more of a "kernel" issue than the Virtual Box issue.   
Anybody else experience a similar result with this kernel version?
Any suggestions?