Error in Encrypting web.config connection string

Question

Hi everybody, I am encrypting web.config file. My code is below.

Configuration config = WebConfigurationManager.OpenWebConfiguration("~");
ConfigurationSection section = config.GetSection("connectionStrings");
if (!section.SectionInformation.IsProtected)
{
    section.SectionInformation.ProtectSection("RSAProtectedConfigurationProvider");
    config.Save();
}

but this gives me error

Object already exists. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Security.Cryptography.CryptographicException: Object already exists.