Problems with allineament of the y axis

[mangiamammuth]

I am expieriencing problems as a novice of 3d printing.
After succesfully printing the test model (a sitting dog) and 2 test models that i designed (just cubes basically), i have had problems with the third test model (another cube).
Once the print starts, the bed tries to move but it stops itself as if there was an obstacle in its way, and after a bit it continues to move as if nothing had happened, the print was shifted forward and it went fine for 2 and a half centimetres of the cube's height, then it shifted the print forward again for a quarter of a centimeter, then it proceded normally for another half of a centimeter and than the x axis buged out creating chuncks of plastic on the border of the print.
My 3d printer is a Geeetech A10, with 1 extruder;
board info are: GT2560 V3.0, Baud 250000, HW VER: V2.30, Protocol: 1.0, PSU: Generic;
software is :A10_G05(GT2560V4+CH340), version V1.1.8-V2.0,

I've uploaded 3 pictures of the third model i made for reference (It should be a poligon whith a slope dug in it).

if you have any advice please tell me.

thank you in advance.