Search your application’s product name inside
"C:\Users \#Username#\AppData\Local" and delete user.config, then Start your app again.
There are some other special directories which are also contains the temp config files.
VB.NET Code : Label1.Text = My.Computer.FileSystem.SpecialDirectories.AllUsersApplicationData
Result is [w10 64-bit] = C:\ProgramData\Microsoft\WindowsApplication1\126.96.36.199
Result is [w10 64-bit] = C:\ProgramData
VB.NET Code : Label2.Text = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData)
Result is [w10 64-bit] = C:\Users\venice\AppData\Local
VB.NET Code : Label2.Text = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData)
Result is [w10 64-bit] = C:\Users\venice\AppData\Roaming
Note : Results will be same if OS (W7 64-bit, w8 64-bit)
If there is no user.config then also it throws this error.
Go through this article : The exception was configuration system failed to initialize.