After upgrading VirtualBox to version 4.3.10, you may find some or all of your virtual machines won't start, with an error message to the screen, including the error code NS_ERROR_CALL_FAILED 0x800706be.

While this may happen on a Windows host, I've only ever noted it on Linux hosts - although considering I've only got a single Windows host running, it's not really surprising that I wouldn't have seen it. If you check the log of a non-starting VM, the last few lines will look like this:

00:00:02.018323 Activating Local APIC
00:00:02.018364 CPUM: SetGuestCpuIdFeature: Enabled APIC
00:00:02.018935 PIT: mode=3 count=0x10000 (65536) - 18.20 Hz (ch=0)
00:00:02.024902 Shared Folders service loaded.
00:00:02.051791 thread routine failed the initialization

The last line is the important part.

This seems to be caused by a failure to read the hard drive image file properly.  Simply compacting the hard drive from the command line usually fixes it.

First, shut down all VirtualBox processes, killing them through the top command, if necessary. Then, use this command:

vboxmanage modifyhd VirtualBox\ VMs/<VM name>/<VM hard drive file.vdi> --compact

where <VM name> is the folder your VM is stored in, and <VM hard drive file.vdi> is the file containing the hard drive image for the affected VM.

This may take a few minutes, depending on the size of the virtual hard drive, but once it's finished, you should be able to restart VirtualBox, and your VM should start properly.

I ran across an error in a Knowledgetree plugin while setting it up for a client.  For those who don't know, Knowledgetree is an open source document management system.

Two plugins were installed, the Wemag TreeBrowse plugin, and the Wemag Online Document Viewer.

The Treeview plugin was installed first, and worked as expected for several days.  However, when the Online Document Viewer was installed, Knowledgetree immediately failed with an error:

Fatal error: Class 'KTFolderAction' not found in /usr/share/knowledgetree-ce/plugins/WemagTreeBrowsePlugin/WemagTreeBrowsePlugin.php on line 34

Note the error appears to be in the TreeBrowse plugin, but only appears once the Online Document Viewer is installed.

Although I haven't analyzed the code execution path, or the complete list of loaded libraries and included files, it appears that these two plugins load in such a way as the function include files are not loaded in time for the TreeBrowse plugin to use them when both are installed.

The missing function - KTFolderAction - is defined in a function library that comes with Knowledgetree, in the standard library directory:

/actions/folderaction.inc.php

The easiest solution is to include this file within the WemagTreeBrowsePlugin.php file prior to the point where the function is needed.

In the WemagTreeBrowsePlugin.php file, starting on line 26, is a series of library include statements:

require_once(KT_LIB_DIR . '/plugins/plugin.inc.php');
require_once(KT_LIB_DIR . '/browse/PartialQuery.inc.php');
require_once(KT_LIB_DIR . '/documentmanagement/Document.inc');

Add in an extra one at the end, so that the series looks like this:

require_once(KT_LIB_DIR . '/plugins/plugin.inc.php');
require_once(KT_LIB_DIR . '/browse/PartialQuery.inc.php');
require_once(KT_LIB_DIR . '/documentmanagement/Document.inc');
require_once(KT_LIB_DIR . '/actions/folderaction.inc.php');

This fixes the missing function error, and allows you to login.  Both plugins also work properly, so no functionality is broken by this solution.

Occasionally, when trying to join a Windows-based computer to a Windows Server domain, the configuration options needed are greyed out and disabled.

This can be caused by at least two things:

• the "Client for Microsoft Networks" option is disabled for the network interface.
• the "Computer Browser, "NetLogon" or "Workstation" services are not running.

I mostly see these services disabled on home computers that were used for gaming, replaced, which are then brought into a small business for a lightweight or temporary role.  Disabling these services causes no issues on a standalone computer, as they are not needed, and it can increase performance slightly for gaming to eliminate the small overhead of these services.

To enable them, start the computer management console (Right click "Computer/My Computer" in the Start Menu, and select "Manage"), select Services in the left hand side tree, and find the three services listed.  Check to see they're all set to auto start, and that they're currently running.

If you're using the Mozilla Thunderbird email program, you may have noticed that you get an error like this:

The current operation on "INBOX" did not succeed. The mail server for account <my email server> responded - nz number.

when you try to view an email with certain attachment types.

If you're also running AVG Antivirus 2011, this error is caused by the email scanning functionality of AVG.  Other antivirus software might also trigger this error, but I've only ever seen it with the free version of AVG, although it's reasonable to assume that the AVG Internet Security, or other commercial versions of AVG would also cause this problem.

This can be tested by disabling incoming email scanning in the AVG interface.