FileTransfer error: Read-Only filesystem

D/FileTransfer(12423): download http://example.com/image.jpeg to //avatar.jpeg
E/FileTransfer(12423): {"target":"\/\/avatar.jpeg","source":"http:\/\/example.com\/image.jpeg","http_status":0,"code":1}
E/FileTransfer(12423): java.io.FileNotFoundException: /avatar.jpeg: open failed: EROFS (Read-only file system)
E/FileTransfer(12423): 	at libcore.io.IoBridge.open(IoBridge.java:409)
E/FileTransfer(12423): 	at java.io.FileOutputStream.<init>(FileOutputStream.java:88)
E/FileTransfer(12423): 	at org.apache.cordova.CordovaResourceApi.openOutputStream(CordovaResourceApi.java:293)
E/FileTransfer(12423): 	at org.apache.cordova.CordovaResourceApi.openOutputStream(CordovaResourceApi.java:274)
E/FileTransfer(12423): 	at org.apache.cordova.filetransfer.FileTransfer$4.run(FileTransfer.java:708)
E/FileTransfer(12423): 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
E/FileTransfer(12423): 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
E/FileTransfer(12423): 	at java.lang.Thread.run(Thread.java:841)
E/FileTransfer(12423): Caused by: libcore.io.ErrnoException: open failed: EROFS (Read-only file system)
E/FileTransfer(12423): 	at libcore.io.Posix.open(Native Method)
E/FileTransfer(12423): 	at libcore.io.BlockGuardOs.open(BlockGuardOs.java:110)
E/FileTransfer(12423): 	at libcore.io.IoBridge.open(IoBridge.java:393)
E/FileTransfer(12423): 	... 7 more