Android Exception getInputStream() is not available

Hello community !

We have launched an Android game made with Unity on the Android Market and got some errors from users in our report manager, and one with web request, here is the log :

 java.lang.IllegalStateException: getInputStream() is not available. Is this a reentrant call?
        at org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:524)
        at org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnectionImpl.getHeaderField(HttpURLConnectionImpl.java:464)
        at java.net.URLConnection.getHeaderFieldInt(URLConnection.java:572)
        at java.net.URLConnection.getContentLength(URLConnection.java:335)
        at com.unity3d.player.WWW.run(Unknown Source)

Does anybody know where it comes from ?

Thanks !