Failed to lock index buffer in CMeshDX8::LockIndexBuffer

http://support.steampowered.com/cgi-bin/steampowered.cfg/php/enduser/std_adp.php?p_faqid=420

Cause

The Failed to lock index buffer error will occur when you use Alt+Tab to switch between windows while playing a game and your machine is unable to allocate sufficient memory to render graphics when you switch back to your game window.

The best solution for this behavior is to properly exit the game to return to your desktop so you may work with other applications.

ATI Video Card Users

This issue may also be related to an outdated driver for your video card. To address this issue, it is recommended that you uninstall your current Catalyst drivers, then install the latest Catalyst drivers.

1. Download the ATI Catalyst Uninstaller
2. Install the Latest ATI Catalyst Drivers