You put the wrong version of TWRP on your tablet probably? when you restart and it boots into TWRP, on the starting screen you should be able to use fastboot.
---------- Post added at 04:33 PM ---------- Previous post was at 04:31 PM ----------
When it happened to me, it was a bootloader and TWRP conflict: I flashed the jb version instead of the -42 Version. to fix it, I did fastboot reboot bootloader and then got back into android and flashed the correct one from Terminal Emulator. Or you could just flash it from there.
I''m on WIN7 64...... like I said I boot it up, all I needed is command : abd reboot-bootloader
that cat me in bootloader mode, with http://forum.xda-developers.com/show...56634965818376
I boot it up on stock 4.2.1 JOP40D.ww_epad-10.6.1.8-20130225
sorry for trouble ...... thanks all for trying to help ....