Ok, so I'm getting splinters from scratching my head so I'm going to ask for help:
New and clean install as SUB domain of main site demo.mystore. com
Admin works fine, as does store front IF url has /index.php included, click on logo or simply have demo.mystore. com as url and I get a 404 error.
Something in configure.php I'm guessing, but what?

Thanks in advance.