Import project into new project and see if you can save it under a different name.
I tried that but still can't save. Even created a blank 'new project' and still won't let me save.
It appears something gone corrupt in the application itself.
This is the message I get:
Project Save Error.
An unkown error occured while saving the project. Select 'Save As' from the File menu to
save the project to a new location.
Last minute break through...
I followed sombody elses advice on a different forum to re-start while holding a SHIFT key
to reset the cache.
I could save the project straight after but when I tried creating MPEG2 DVD it would give me
an error and the above would start all over again.