如题，我先把报错原因粘贴过来
07-24 03:25:07.898: ERROR/D.E. FILE NOT FOUND(1360): /sdcard/2499_com.mobi.filemanager.activity_142051.apk (Permission denied)
07-24 03:25:07.908: ERROR/D.E. IO(1360): /sdcard/2499_com.mobi.filemanager.activity_142051.apk (Permission denied)
07-24 03:25:07.908: ERROR/D.E. IO(1360): java.io.IOException: /sdcard/2499_com.mobi.filemanager.activity_142051.apk (Permission denied)
07-24 03:25:07.908: ERROR/D.E. IO(1360): at sfa.mobroad.mdm.function.DownloadCallable.downFile(DownloadCallable.java:114)
07-24 03:25:07.908: ERROR/D.E. IO(1360): at sfa.mobroad.mdm.function.DownloadCallable.doDownload(DownloadCallable.java:50)
07-24 03:25:07.908: ERROR/D.E. IO(1360): at sfa.mobroad.mdm.function.DownloadCallable.call(DownloadCallable.java:42)
07-24 03:25:07.908: ERROR/D.E. IO(1360): at sfa.mobroad.mdm.function.DownloadCallable.call(DownloadCallable.java:1)
07-24 03:25:07.908: ERROR/D.E. IO(1360): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
07-24 03:25:07.908: ERROR/D.E. IO(1360): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
07-24 03:25:07.908: ERROR/D.E. IO(1360): at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
07-24 03:25:07.908: ERROR/D.E. IO(1360): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
07-24 03:25:07.908: ERROR/D.E. IO(1360): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
07-24 03:25:07.908: ERROR/D.E. IO(1360): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
07-24 03:25:07.908: ERROR/D.E. IO(1360): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
07-24 03:25:07.908: ERROR/D.E. IO(1360): at java.lang.Thread.run(Thread.java:1096)
我想把一个APK程序下载到SD卡中，但是出了这个错误。
我在manifest里添加了android.permission.WRITE_EXTERNAL_STORAGE，而且也不是内存不足，因为我用的物理机去做的测试。
我不知道有没有人用过系统签名，我的程序在用系统签名签名之前是可以运行的，但是用调用系统签名之后程序就跑不起来了。。。
按道理来说系统拥有最高权限，我调用系统签名也是为了实现静默安装，但是没想到在却提示权限不足。
求解，在线等，急！！！！
------解决方案--------------------
加上
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>