To reproduce the problem:

1-) Go to a Space Page
2-) Click Edit
3-) Select the Rich Text Editor tab
4-) Click on the Add Emoticon menu icon
5-) Choose the Smile Face
6-) An SSL error will be displayed with the message: "You are trying to access a non secure content. Do you want to display the non secure content?"

After talking to DOS, was concluded that it is related to a known IE6 problem related to iFrames.

Workaround being proposed: Change IE6 settings, disabling the Warn if changing between secure and not secure mode option.