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I uninstalled VB 4.3.10 and my VM, then I installed VB 4.2.26 and its extension. I created a new VM with Lubuntu and installed the GA. I can now access my usb drive and SD card, but
the disto window is still small after a few reboots.:

Which version of Lubuntu?

Version 14.04

did you remember to install dkms and build-essential? if not, install them then reinstall the guest additions and restart the guest.

The 4.2.26 guest additions should work correctly although I am using 4.3.14.

I ran these four steps again:

1. sudo apt-get install dkms build-essential linux-headers-generic
2. Devices > Install Guest Additions
3. sudo /media/luis/VBOXADDITIONS_4.2.26_95022/VBoxLinuxAdditions.run
4. sudo apt-get update && upgrade

Yet I still have the problem.

Advice Pro wrote:I ran these four steps again:

1. sudo apt-get install dkms build-essential linux-headers-generic
2. Devices > Install Guest Additions
3. sudo /media/luis/VBOXADDITIONS_4.2.26_95022/VBoxLinuxAdditions.run
4. sudo apt-get update && upgrade

Yet I still have the problem.

My guess is the 4.2.26 guest additions won't build with the kernel or xserver for Lubuntu 14.04. So you would need to update VirtualBox. If you are using a Windows host, then update to 4.3.12. If you are using a Linux or Mac host, update to 4.3.14.

btw, your No. 4 step shouldn't run at all and you should update first, not last.

I prompted the OP several messages back to provide a VM log file - Minimum information needed for assistance.

I see that has not happened, so it's no surprise that this thread meanders on without reaching a conclusion. We shouldn't need to guessing what host OS is involved, or whether the GAs are installed. @AdvicePro - please provide the information requested.

I uninstalled VB 4.2.26 with extension pack and Lubuntu VM, then installed VB 4.3.14 with extension pack and created a new Lubuntu VM with GA. The guest desktop does open bigger, But still not As big as it usually is:
I've attached the log.

Look at your screen shot and the phrase guest additions.

You have the guest additions ISO mounted in the virtual CD drive, but the GAs have not actually been installed. Please read chapter 4 of the user manual for installation instructions.