I don't think you read his question. I am having the same problem:
1) I downloaded a trial version of Sitefinity and created a project locally.
2) I published the web project to a development server.
3) When I attempted to access the server URL, and began the Project Startup process, after submitting my license key, it prompted me for a database.
4) I CHOSE SQL EXPRESS. Which means that Sitefinity created the database.
5) The startup failed with the following error:
There was an error trying to connect to the Database Server:
Could not connect to server.