When you activate the lists and wikis radEditor feature from the site collection features, we try to copy a file called RadEditorList.ascx
from the feature folder, e.g.:c:\Program Files\Common Files\Microsoft Shared\web server extensions\12\TEMPLATE\FEATURES\RadEditorFeature\
to the control templates folder c:\Program Files\Common Files\Microsoft Shared\web server extensions\12\TEMPLATE\CONTROLTEMPLATES\
I suppose, that for some reason the RadEditorFeature folder might not be deployed on all servers in the farm. This means that you will need to copy the file to the control templates folder on each server in order to use the feature.
Looking at the deployment instructions for the editor, I also see that you will need to reset IIS after you activate/deactivate the feature in order to clear the MOSS cache. Are you doing this on all servers on the farm?
Thank you for reporting this issue, we will further look into it to see what is the exact cause.