PHP MD5 to .NET C#

Hi all,

I am in a project where I need to create a MD5 login that works like the PHP MD5 function. I have set this up and it seems to work but the results are not coming out the same. What I mean is the same login using the "PHP MD5" hashed password does not match the .NET hashed password. Both are taking a salt and the password and then creating the hash but the results are different for the same entered password.
 

Simple PHP CODE:
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function encryptString($string) {
    return  md5($string . PASSWORD_SALT);
}
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PASSWORD_SALT is a defined constant with the value (without the quotes) = 'TheSalt'
$string is what is entered in the password field.
 
 

.NET CODE:
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...