Reaper won't render -output file problem?

[Pleshplat]

Hi,

Im a new user- and I've encountered a quite basic problem.

Reaper won't render.

When i try to render a project, i get to the rendering file window- which says 'output file - no output'

And below that -

'Render status:
The target drive/path does not exist, is unavailable or in use'.

I've kept the output file directory and 'render to' settings at default- ie, sending to the Reaper Media folder. I've also tried changing them to no effect.

I've tried uninstalling reaper, and reinstalling.

Any suggestions from the community?

Many thanks-

(I'm using 10.7.3 on a macbook pro. And the Reaper 64 bit version. )