Darwinia asks you to use alt-tab to control the Task Manager in game. On some Windows systems this can cause problems.

If you are running Windows Power Tools, try disabling this as it can cause problems with the ALT-TAB in game. You can disable it simply by bringing up the Windows Task Manager (by pressing CTRL-ALT-DEL simultaniously) and terminating the task named "taskswitch.exe". Or you can just uninstall the TaskSwitch powertoy.

If you are running any other program that uses Alt-Tab in some special way, try disabling this.

If you are still having problems, you can press Ctrl-Alt-Tab in game instead of Alt-Tab. It's a bit awkward but will solve your problem until we can address it properly in a future patch.

But what do I do if I want to actually alt-tab out of the game? My boss might see me playing Darwinia...

You can minimise Darwinia by pressing alt-escape.