I have been having this same problem, "Lenovo Thinkvantage Toolbox has stopped working," on my T400 and now its replacement, the T420, for two years now.
I found this discussion and decided to try the recommended uninstall/reinstall and post my results, since no one else has. I uninstalled and and navigated to the recommended location at support.lenovo.com. There, I found a tool that I assumed would provide a way to download the new Thinkvantage Toolbox installer. It was way to complicated, wanted to download a tool just to identify the model of notebook I have.
After I downloaded the tool and identified my system, how to download the actual Thinkvantage toolbox was not clear. I finally found a download for it, version 1.0.5812.9.
I downloaded and began the install. It installed, or started installing, version 6.0.5849.23 of Toolbox. It repeatedly (three times, maybe) displayed the "Lenovo Thinkvantage Toolbox has stopped working" message during the install, but did show a "install completed message" or something like that, eventually.
When I try to start the Toolbox by clicking the icon on the taskbar, it keeped crashing. So, I uninstalled it again, with the intent of rebooting before re-installing. It generated the "Lenovo Thinkvantage Toolbox has stopped working" message during the uninstall. It showed an uninstall completed message.
I rebooted. I started a re-install and the progress bar quickly went to about half complete, sat there for about a minute, then showed a complete box, of some kind.
At the same time, it threw up a “Thinkvantage Toolbox has stopped working” message.
When I click the thinkvantage button on the taskbar, it starts the app, shows the "Starting" splashbox, then the GUI and then crashes. Very disappointing.
Bruce
