101652 No database selected at row 6

I am looking for someone to help with the installation of a php classified ad script into my subdomain. It is ticking me off. There are some instructions with it. I keep getting the error "No database selected at row 6" I would like the person to walk me through what the heck happened so I will be able to install this on my own next time. I am not too dense (I think) I have installed scripts before. but this one has got me stumpted Thankyou, Bernie