I have the same problem..
I have a Blu Dash 3.5 D161a with android 4.2.2. This cellphone has been bought from the network provider, it starts with the network provider's logo instead of the blu's logo. I can enter in fastboot mode and I'm able to see my device from adb, but when I type fastboot erase recovery or fastboot erase system it gets stuck on erasing.
Is the booloader locked or something like that?