There are several facets to ActiveX problems affecting ESRIs ArcGIS Toolbox. Most impact Internet Explorer ActiveX scripting or XSL of tools making calls to IE scripting. All running in the Local Security zone. These misconfigurations can impact Microsoft control panel (.CPL) and management console (.MSC) snap-ins in addition to non-Microsoft applications.
Some repairs involve verifying correct permission for the My Computer -- Zone 0 use of feature 1200 & 1400--corresponding to permit Run ActiveX controls and plug-ins or Active scripting respectively. The full listing (through IE7 is here) Microsoft KB 182569 IE8 & now IE9 have additional Zone keys.
The pseudonumeric key (inverted - L) is called a "parasite" security zone by Microsoft. An Adobe Flash upgrade has been mentioned as the culprit--but that is not proven. None the less, removal of the parasite security zone (if present) from the HKCU and HKLM Internet Settings keys is the Microsoft recommended repair to restore function to Local Zone 0 ActiveX dependent programs--like the ArcGIS Toolboxes.
It is safe. Microsoft now provides Hot Fix support in Microsoft KB 2506343