Not able to edit properly in editable area when template is applied

[gtbikerider]

Dreamweaver seems to be playing up lately! When I try to edit a page that has a template applied I can make the edit but I get the message...

"You have made changes to code that is not marked as editable. If you retain those changes, they will be lost the next time you apply a template update to this file. Do you want to retain the changes until then?"

...and my edits are discarded. This happens on many pages and sites.

The code I'm editing is well within an area surrounded by...

<!-- InstanceBeginEditable name="body" -->
some code
Trying to edit here
some code
<!-- InstanceEndEditable-->


Any ideas what's causing this?

--
John