Function WriteToFile(ByVal mytext As String, ByVal filepath As String, ByVal filename As String) As Boolean
...
End Function

Problem is here:

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
WriteToFile('test.txt','\\servername\c$\','\\servername\f$\inetpub\wwwroot\sss\sss\mainten ance\sss\sss\mnt_input\sss_input.txt')
End Sub

Error: Expression Expected.