Hello everyone;

I have a function which makes a merge TXT files ; this go through different folders and taking txt files in each folder is then join the files.

The issue that I have is that after the function makes scanning all folders , the function generates the following eror :

An unhandled exception of type 'System.IO.IOException' occurred in mscorlib.dll
Additional information: The process cannot access the file 'C:\Users\liderapp\Documents\Scripts\Octubre2015\CM.TXT' because it is being used by another process.

The function is:

For Each topDir As DirectoryInfo In New DirectoryInfo(sourceDir).GetDirectories("*", SearchOption.TopDirectoryOnly)
For Each subDir As DirectoryInfo In topDir.GetDirectories("*", SearchOption.AllDirectories)
For Each txtfile As FileInfo In topDir.GetFiles("*.txt", SearchOption.AllDirectories)
If txtfile.Name.Equals(NameCM, StringComparison.OrdinalIgnoreCase) Then
curFilename = NameCM
ElseIf txtfile.Name.Equals(NameGL, StringComparison.OrdinalIgnoreCase) Then
curFilename = NameGL
ElseIf txtfile.Name.Equals(NameImp60, StringComparison.OrdinalIgnoreCase) Then
curFilename = NameImp60
ElseIf txtfile.Name.Equals(NameImp61, StringComparison.OrdinalIgnoreCase) Then
curFilename = NameImp61
ElseIf txtfile.Name.Equals(NameImp62, StringComparison.OrdinalIgnoreCase) Then
curFilename = NameImp62
ElseIf txtfile.Name.Equals(NameImp63, StringComparison.OrdinalIgnoreCase) Then
curFilename = NameImp63
Else
curFilename = String.Empty
End If
If Not String.IsNullOrEmpty(curFilename) Then
Debug.WriteLine(topDir.FullName)
Debug.WriteLine(subDir.FullName)
Debug.WriteLine(txtfile.FullName)
Debug.WriteLine(Path.Combine(topDir.FullName, curFilename))
Using sr As StreamReader = txtfile.OpenText
File.AppendAllText(Path.Combine(topDir.FullName, curFilename), sr.ReadToEnd, Encoding.Default)
End Using
End If
Next txtfile
Next subDir
Next topDir

The issue happen when the scaning process finish and occur in this sentences:
File.AppendAllText(Path.Combine(topDir.FullName, curFilename), sr.ReadToEnd, Encoding.Default)

How I can avoid the error ?

TIA