In spite of the number of posts this issue does not seem to have been resolved.
I have a number of .odt files which can be loaded and edited in Open Office but the above error is issued when saving. Other files load and save without problems. Occasionally I can save an affected file in .doc format. The affected files load and save correctly on a different computer
I conclude that there is nothing the matter with either OO or the file but that something in the computer is preventing OO from writing to the content.xml file. I am using a newly installed Open Office version 4.1.3 under Windows 7 with Avast anti-virus. I have tried resetting my OO user profile. This behaviour has only recently started but, other than installing DropBox, I cannot think of anything which I have done which can have altered the configuration of my computer.
I am desperate for help as this error is totally preventing me from proceeding with my work.