Why I am getting Unspeicified error on trying to create a pfx certificate in c#?

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C#

.NET

x509

Why I am getting Unspeicified error on trying to create a pfx certificate in c#?

My Code is as below:
X509Certificate2 certificate = new X509Certificate2(@"D:\testcert1.pfx", "password", X509KeyStorageFlags.MachineKeySet);
&
X509Store store = new X509Store(StoreName.My);
store.Open(OpenFlags.ReadWrite);
store.Add(certificate);