guest additions not working in fedora 20

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I am working on an HP Pavilion dv6 computer with the Windows 7 Home Premium OS. I have installed VirtualBox version 4.3.20 r96997 as well as the 4.3.20 Extension pack. I have installed a Fedora virtual machine in it from a Fedora-20-i386-DVD.iso. Once it was completely installed, I started it up, opened a terminal window, su to root, then executed the following commands: yum -y update, I restarted the fedora machine, yum install gcc dkms kernel-devel, Then from the menu: Devices->Install Guest Additions CD Image..., then run, The guest additions install. I restarted the fedora machine. The guest additions don't work: when I resize the window, the fedora desktop does not resize. Any idea what could be wrong?

Since that doesn't seem to work, I have installed a Fedora virtual machine in it from a Fedora-20-x86_64-DVD.iso file. I went through the same process, but when I tried to restart after installing the guest additions, it fails with the following error: "The instruction at 0x079285e4 referenced memory at 0x00000028. The memory could not be read. Click on OK to terminate the program."

Again, any idea what is wrong?