Error: Could not use "file name"; file already in use.

I wrote a solution for you. I think you should use this sample that I did:

1. Open a new Visual C# .NET console application.
2. In Solution Explorer, right-click the References node and select Add Reference.
3. On the COM tab, select Microsoft ADO Ext. 2.7 for DDL and Security, click Select to add it to the Selected Components, and then click OK.

        public static void Main()
        {
            DataBaseManager dataBaseManager = new DataBaseManager("Marat_Beiner");
            OleDbConnection connection = dataBaseManager.ConnectToDatabase();
            Console.ReadKey();
        }

        public class DataBaseManager
        {
            private readonly string userName = "anonymous";
            private string dbFilePath = String.Empty;
            private string dbCnnectionString = String.Empty;
            ADOX.Catalog catalog;

            public DataBaseManager(string userName)
            {
                this.userName = userName;
                this.dbFilePath = String.Format("{0}\\{1}.accdb", Environment.CurrentDirectory, this.userName);

                this.catalog = new ADOX.Catalog();

                this.dbCnnectionString = String.Format("Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};", this.dbFilePath);

                if (!File.Exists(this.dbFilePath))
                {
                    this.catalog.Create(this.dbCnnectionString);
                    Console.WriteLine("Database Created Successfully");
                }
                else
                {
                    Console.WriteLine("Database Inicialized Successfully");
                }
            }

            public OleDbConnection ConnectToDatabase()
            {
                OleDbConnection oleDbConnection = new OleDbConnection(this.dbCnnectionString);
                Console.WriteLine("Database Connected Successfully");
                return oleDbConnection;
            }
        }

In this sample the DataBaseManager creates Access database with file name equals user name.

Your solution is bad if you create a binary file for using with OleDbConnection class.

You did one mistake in your code:

         DataBaseManager.conn = new OleDbConnection(this.dbConnPath);
            if (DataBaseManager.conn == null)
            {
                MessageBox.Show("Can't connect to database", "WorkManager", MessageBoxButtons.OK, MessageBoxIcon.Information);
            }

The statement is incorrect and this will never happen.

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That might creates the problem.

FileStream fs; //still in memory, didnt disposed. change your code to..

using (FileStream fs = File.Create(Environment.CurrentDirectory + "\\" + userName + ".accdb"))

The file exists, and I think it's open (because the exception says that it in use).
The declaration of "fs" is above as private.

Environment.CurrentDirectory points to the Debug Folder if you are running the application in the Debug mode.
Make sure your file exists amd not opened in memory. Also, where is your FileStream declaration method?

using (FileStream fs = File.Create(Environment.CurrentDirectory + "\\" + userName + ".accdb"))
 {
 }

Here, I did it, and still nothing

public DataBaseManager(String userName)
        {
            this.userName = userName;
            if (!File.Exists(Environment.CurrentDirectory + "\\" + userName + ".accdb"))
            {
                using (fs = File.Create(Environment.CurrentDirectory + "\\" + userName + ".accdb"))
                {
                   
                }
            }
        }

        public void connectToDatabase()
        {
            DataBaseManager.conn = new OleDbConnection(this.dbConnPath);
            if (DataBaseManager.conn == null)
            {
                MessageBox.Show("Can't connect to database", "WorkManager", MessageBoxButtons.OK, MessageBoxIcon.Information);
            }
            else
            {
                String state = DataBaseManager.conn.State.ToString();
                using (File.Open(Environment.CurrentDirectory + "\\" + userName + ".accdb", FileMode.Open))
                {
                    if (state.Equals("Closed"))
                    {
                        DataBaseManager.conn.Open();
                    }
                }       
            }
        }

Hi,
I am focussing on "file already in use" problem. On creating a new file, it will be locked by a stream object, which you need to close manually. A "using" block will do it automatically and the file you created is then free to use. Tried that?

The goal:
I wont to create for every user his private data base, thus after I've received his user name I create an accdb file for him, connect to this data base and create tables.
The problem:
after I create the file it won't connect to it, it throws an exception at line :DataBaseManager.conn.Open();, says that the file already open.

You can't connect to the file by using DataBaseManager.conn.Open(); if you use File.Create("accdb ") method.  DataBaseManager you can use only connect to the data bases.

System.Data.DbManager DbMgr = new System.Data.DbManager("System.Data.OleDb", connstring);

If you want to operate with File.Create() created file you could do it like in my sample.

Maybe could you write more details about problem for better understanding

        public static void Main()
        {
            string path = @"accdb";

            // Delete the file if it exists.
            if (File.Exists(path))
            {
                File.Delete(path);
            }
       
            // Create the file.
            using (FileStream fs = File.Create(path))
            {
                Byte[] info = new UTF8Encoding(true).GetBytes("This is some text in the file.");
                // Add some information to the file.
                fs.Write(info, 0, info.Length);
            }

            // Open the stream and read it back.
            using (StreamReader sr = File.OpenText(path))
            {
                string s = "";
                while ((s = sr.ReadLine()) != null)
                {
                    Console.WriteLine(s);
                }
            }
        }

Do you mean that I need to open the file when I want to connect to the data base (before I write: "DataBaseManager.conn.Open();")?

I've tried it, didn't help.

Hi,
You need to close the stream after file creation. Make sure to use "using" block like below.
using (File.Create("<<>>"))
{
   
}
//From here only open the created file. Make that also in another "using" block.