Invisible Editor

I've installed FCKEditor on around a dozen sites to date. And they've all been fine.

I have one site however I have a problem with. I do the install, associated permissions, etc.

Then I go to create new content, and FCKEditor simply isn't there, hanging above the text box. But everything up to this step has been fine.

Here's the interesting bit - when I enter text into the body area, and then save and view the node, the text I put in is no longer there. So it's like the editor is invisible almost - it's preventing the body area from saving any text.

Once I disable the module, this issues goes away.

I wonder if I've stumbled upon an incompatbility with another module? Or perhaps it's something else? I've compared this install to a number of others, and I can't see any difference in settings / processes that I've done.

I like FCKEditor (looking forwards to CKEditor) but I might have to resort to another option, unless anyone's got any ideas? Thanks for your help.