Editing pages

The way you've described it, the solution lies in figuring out what's different on the page where it doesn't save. It's also worth noting whether it used to work and now doesn't, and whether it happens in all browsers. Nowadays most FCKeditor problems lie in browser incompatibilities. As newer browser versions come out FCKeditor becomes more problematic because it's not maintained anymore - one of the perks of using a product that's constantly maintained (CKEditor 3).