The site is upgraded in different steps, dont remember exactly. The problem occured after upgrading from "5.2.375.133" to "5.2.375.226". After what I can see the edit-mode still works correctly but the warning is there about error "800a025e".
"Googling" gives hits about the error and FCKEditor and IE.
Nice catch, we actually fixed it just a few hours ago and the fix will be part of the final SP2 release.
The error says row "2485" and I think the source is TableEdit.js (not sure).
Opening the editpanel in a separate window do not give an error. (http://machinename/SecureUI/edit/EditPanel.aspx?id=1111)
"Jesus" that was fast. I saw your reply first after sending some more comments.
Thank you very much Per, that feels good.