AssetsManager error when downloading assets via gprs network

Hi, I am trying to download some content from the server using AssetsManager via gprs network, the code is as below:
@
AssetsManager* pAssetsManager = new AssetsManager( packageUrl, versionFileUrl);
pAssetsManager->update();
@

and I check the console log:
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Cocos2d: there is a new version: 4.30
Cocos2d: downloading… 0
Cocos2d: downloading… 0
Cocos2d: downloading… 0
Cocos2d: downloading… 0
Cocos2d: downloading… 0
Cocos2d: downloading… 0
Cocos2d: succeed downloading package http://www.xx.com/updatePackage.zip
Cocos2d: can not open downloaded zip file /var/mobile/Applications/F42B9733-E08A-46BC-B4E7-DBBA8E110CE6/Documents/cocos2dx-update-temp-package.zip
@

The downloading percent is 0 but It says the content has been successfully downloaded and can’t be unzipped. I checked the cocos2dx-update-temp-package.zip, the file size is 0 bytes!
But the code works fine via wifi network, the zip file can be downloaded and unzipped.
Can anyone help? cocos2d-2.1rc0-x-2.1.2 on ios platform, thanks.

i have same issue, with all sort of networks wifi, lan ,gprs please help.