Paypal DoDirectPayment方法在中等可信托管环境中实施？

Question

我正在使用ASP.NET MVC 3应用程序并使用Paypal SDK for Paypal Website Pro。

我已经创建了如下的API凭据。

using System;
using com.paypal.sdk.services;

using com.paypal.sdk.profiles;
using com.paypal.sdk.util;
/**

 */
namespace GenerateCodeNVP
{
public class DoDirectPayment
{
    public DoDirectPayment()
    {
    }
    public string DoDirectPaymentCode(string paymentAction,string amount,string     
creditCardType,string creditCardNumber,string expdate_month,string cvv2Number,string 
firstName,string lastName,string address1,string city,string state,string zip,string 
countryCode,string currencyCode)
    {
        NVPCallerServices caller = new NVPCallerServices();
        IAPIProfile profile = ProfileFactory.createSignatureAPIProfile();
        /*
         WARNING: Do not embed plaintext credentials in your application code.
         Doing so is insecure and against best practices.
         Your API credentials must be handled securely. Please consider
         encrypting them for use in any production environment, and ensure
         that only authorized individuals may view or modify them.
         */

        // Set up your API credentials, PayPal end point, API operation and version.
        profile.APIUsername = "sdk-three_api1.sdk.com";
        profile.APIPassword = "QFZCWN5HZM8VBG7Q";
        profile.APISignature = 
"AVGidzoSQiGWu.lGj3z15HLczXaaAcK6imHawrjefqgclVwBe8imgCHZ";
        profile.Environment="sandbox";
        caller.APIProfile = profile;

        NVPCodec encoder = new NVPCodec();
        encoder["VERSION"] =  "51.0";   
        encoder["METHOD"] =  "DoDirectPayment";

        // Add request-specific fields to the request.
        encoder["PAYMENTACTION"] =  paymentAction;
        encoder["AMT"] =  amount;
        encoder["CREDITCARDTYPE"] =  creditCardType;        
        encoder["ACCT"] =  creditCardNumber;                        
        encoder["EXPDATE"] =  expdate_month;
        encoder["CVV2"] =  cvv2Number;
        encoder["FIRSTNAME"] =  firstName;
        encoder["LASTNAME"] =  lastName;                                        
        encoder["STREET"] =  address1;
        encoder["CITY"] =  city;    
        encoder["STATE"] =  state;          
        encoder["ZIP"] =  zip;  
        encoder["COUNTRYCODE"] = countryCode;
        encoder["CURRENCYCODE"] =  currencyCode;    

        // Execute the API operation and obtain the response.
        string pStrrequestforNvp= encoder.Encode();
        string pStresponsenvp=caller.Call(pStrrequestforNvp);

        NVPCodec decoder = new NVPCodec();
        decoder.Decode(pStresponsenvp);
        return decoder["ACK"];

    }
}

}

但有些我不能获得成功因为paypal sdk给了我一个中等信任问题。

错误说明是：

That assembly does not allow partially trusted callers

有没有人知道我应该如何解决这个问题？

先谢谢。