1. First error in Windows Application log file
FCB::Open failed: Could not open file D:Program FilesMicrosoft SQL ServerMSSQL11.MSSQLSERVERMSSQLDATAMyDB.mdf for file number 1. OS error: 32(The process cannot access the file because it is being used by another process.).
2. Second error.
Error: 17204, Severity: 16, State: 1.
The fix (for me)
ALTER DATABASE MyDB SET ONLINE
See also this.
And this and this command “alter database