Cannot open user default database. Login failed. Login failed for user 'Machine/ASPNET'

question:

Having the same problem and have spent 2 frustrating days trying to figure it out. Project runs from within VS.net OK -- because VS is authenticating as [machine]/ASPNET -- but if I try to run as http://localhost/[application] I just get the "Cannot open user default database..." error. I've created a [machine]/ASPNET user account in SQL Server Express, assigned it to sysadmin role, have set SQL Express to run in mixed-mode, but all to no avail.

 

the way to fix:

 

I had the same use and tried a whole bunch of things, but this is what solved it for me:

- it seems I had the DB still opened inside my IDE (Visual Web Developer Express), in the database explorer. Right-clicking the database and selecting "close connection" fixed it.

Hope this helps.