Can't install Guest Additions on VB

I'm fairly new to Linux and VirtualBox, so bear with me.

I installed Zorin OS and then Guest Additions and it worked fine at first, but after I had updated all my packages it stopped working - I could no longer run it in Seamless mode. If I tried to re-install GA, it said "Unable to mount the CD/DVD image [name of image] Would you like to force mounting of this medium?" Then underneath: "could not mount the media/drive [name] (VERR_PDM_MEDIA_LOCKED)"

The same thing happened with several Ubuntu-based distros I tried, most recently Lubuntu. It works fine prior to updating, but after that I just get error messages.

From the Terminal, I ran sudo sh /media/cdrom/VBoxLinuxAdditions.run, but it says 'Can't open'

Under 'Disks' it says it is mounted. Unmounting and ejecting then retrying doesn't help.

What am I doing wrong?

I'm running the standard "lubuntu-12.10-desktop-i386.iso" on OSX Mountain Lion, allocating 1gb RAM and 8gb disk space.

Instead of installing the guest additions through VirtualBox try installing the package from the Ubuntu repositories on your guest VM.

Code:

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sudo apt-get install virtualbox-ose-guest-utils  virtualbox-ose-guest-x11 virtualbox-ose-guest-dkms

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This way the guest addition modules will automatically recompile every time you update the kernel (which is what is breaking them).

That worked perfectly, thanks. (You need to reboot after installing, of course.)

...so how do I actually view the folders in the guest? Adding them to VB Shared Folders is easy, but they don't show anywhere on the guest machine.

I tried about 10 different ways that I found online, most involving typing a lot in Terminal, but none has worked. The closest I got was creating some extensionless files in /media/ with the names of the folders in Host that I want to share.