I am following the officiel guide from Umbraco: https://our.umbraco.com/documentation/getting-started/setup/upgrading/migrating-to-v8

but when after i insert the database file from my 7.14.1 site, inserting version into status parameters in config file I get an error:

details: it's an MDF file I copy. I tried to copy the connection string from the old site directly. I tried to check folder security, no luck.

I don't know what to do anymore?

Boot failed: Umbraco cannot run. See Umbraco's log file for more details.

-> Umbraco.Core.Exceptions.BootFailedException: A connection string is configured but Umbraco could not connect to the database. at Umbraco.Core.RuntimeState.DetermineRuntimeLevel(IUmbracoDatabaseFactory databaseFactory, ILogger logger) at Umbraco.Core.Runtime.CoreRuntime.DetermineRuntimeLevel(IUmbracoDatabaseFactory databaseFactory, IProfilingLogger profilingLogger) at Umbraco.Core.Runtime.CoreRuntime.Boot(IRegister register, DisposableTimer timer)