ouch... In Pycom's webpage, the last version of DFU that is writen is pytrack_0.0.4.dfu and I do not download because it's the version that I have now: "The latest firmware is v0.0.4. The DFU file can be downloaded from the links below:" But, if open the link, the version is 0.0.6.... Sorry, it's my fault! Works again!