Workarounds:
Remove Extensions Manager From the Control Panels folder
Move the Extensions Manager control panel out of the Control Panels folder. This will prevent the spacebar from activating the Extensions Manager at startup.
Users with access to the Finder, such as yourself, can still open the Extensions Manager and use it without it actually residing in the Control Panel folder. Moving it out of the Control Panel folder will not disable it entirely, it will only disable the spacebar access to it at startup.
Remove Extensions Manager From the Extensions folder
You can also remove the EM Extension itself, which also prevents the spacebar from opening the control panel window at startup. If you do remove the EM Extension, it will no longer be functional. However, At Ease will not let users open this control panel even if they have access to other control panels.
Notes:
1) The EM extension will be at the top of your Extensions folder list if you are viewing by name. It has an extra space in front of its name so that it will load first, before the other extensions.
2) This issue is resolved in the At Ease 3.0.