Error in PrincipalContext.ValidateCredentials

Question

I have used below code to authenticate user with Active Directory.

using (PrincipalContext principalContext1 = new PrincipalContext(ContextType.Domain, domainName))
{
if (principalContext1.ValidateCredentials(userName, password))
{
//code to successful login
}
}

Getting error "The server cannot handle directory requests." in ValidateCredentials method.

I have tried passing contextOptions as third parameter "ContextOptions.Negotiate | ContextOptions.Signing | ContextOptions.Sealing" in ValidateCredentials method.

It resolved my error, but I came to know from msdn that it is default parameter.

 

Why should I need to pass this? Any alternative solutions? Thanks in advance.