Stepper Motor Configuration problem

I tried with 2 stepper motors NEMA 17 and 2 DM420A Controller driver and have the same problem where the stepper motor trembles and can move in.any direction in an alternate way. 
My wirings are A+ A- B+ B- to blue, red, green, black of the stepper motor and DC+ to the 12 volts power and DC- to GND of the same power. The signals PUL to the PIN 2 of the BOB DB25-1205 and DIR to the PIN.3 of the BOB. And +5V to the 5 volts power and ENBL to the grownd of the same.power.  Setting 1,2. 4,5,6,7 ON, 4, OFF      

X AXIS Configuration  

You forgot the visual of your driver step setting (SW1~7). (edit: ah. just noticed the "Setting 1,2. 4,5,6,7 ON, 4, OFF" part.)

When you say "tremble", you mean as in resonance or the motor direction is eratic? I.e. resonance, low cost steppers/drivers are notorious for that, particularly in their 50~150Hz range (natural freq). Before upgrading for half- decent motion I had my mill enclosure sheet metal rattling and screaming for help each and every accel/decel, I swear it sounded like a freight train...

Try: 1:OFF, 2:OFF, 3:OFF,  4:OFF, 5: OFF, 6:OFF, 7:ON. And set this to 8.0 in pconf.
If you still have excessive resonance, your steppers/drives are best in the bin. Re-equipped!

Nothing on that BOB should be wired to 12V, so remove that first.
Do not test or power, just remove the 12V supply !!!! The drives clearly state 5V on the inputs.
If you do need isolation, use two 5V power supplies or use USB power for the side towards parallel port and a power supply for VDD.
Then, change the step time and space to 10000, dir stuff to 20000, and base period to at least 100000.
Those BOB's have really slow optocouplers, so anything under those values will not work at all or work very badly.

Thanks you both.
The problem was with the step time and dir stuff and the base period.
Now it doesn't trembles anymore and the movement is continous. I have to adjust it to the best numbers but you were right.
Great Job
Thanks you both