Most probably the issue is provoked by the fact that the ASPNET
account does not have the popper permissions for the projects database. Sometimes they are not inherited correctly and are causing this problem. We would suggest you to double-check whether the 57CHEVY\ASPNET
account has full permissions for the ~/Sitefinity/WebSites/YourProject/App_Data/Sitefinity_log.ldf
Another possible explanation of the problem could be that it occurs when running the SQL Management Studio
and trying to login in your project simultaneously. The SQL Express database has a limitation of the simultaneous connections which would result in the received error. It could have only one connection at a time, which means that while accessing the Web site the connection has been already used by the SQL Management Studio
Hope this helps.
the Telerik team