struts2 下载出错！IE提示无法下载！

弹出如下的错误提示：

配置如下：

<struts>
<package name="download" extends="struts-default" namespace="/download">
<action name="downloadControlCert" class="com.etaocn.pay.download.DownloadControlCertAction">
<result name="success" type="stream">
<param name="contentType">application/x-x509-ca-cert</param>
<param name="inputName">inputStream</param>
<param name="contentDisposition">attachment;filename="etaoCNControl.cer"</param>
<param name="bufferSize">4096</param>
</result>
</action>
</package>
</struts>

Class如下：

package com.etaocn.pay.download;

import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;

import org.apache.struts2.ServletActionContext;

import com.opensymphony.xwork2.ActionSupport;

public class DownloadControlCertAction extends ActionSupport {

public InputStream getInputStream() throws Exception
{
// File file = new File("/control/etaoCNControl.cer");
return ServletActionContext.getServletContext().getResourceAsStream("/control/etaoCNControl.cer");
// System.err.println(file.getAbsolutePath());
// return f;
}

public String execute() throws Exception {
return SUCCESS;
}

}

不知是什么引起的错误？