I just upgraded to IE10 and found the ENTER key does not work on the forums. This is also true for other browsers like CHROME.
I found it's a known issue with vbulletin forums and the true fix is an update to the forum editor.
There are 2 work arounds I found.
1. Change the editor mode from WSIWYG mode to edit/standard/source mode.
For the LOTRO forums, this is the icon in the upper left menu [a/A]
2. You can copy/paste a line with the <enter> code from another source like notepad as needed.
Hope this helps others with the same issue.