Weird Z Axis Problems

Hi,
yesterday I finished my Prusa I3. Everything seems to work pretty well. The heating elements are heating up, i flashed the firmware and adjusted the steppings. All motors move in the right direction with the right distance. But when it comes to printing, i get a problem which i cant solve. After the homing of the axis, when the extruder and the bed are heated up, my z axis moves up 50mm and the printer starts printing in the air. But when i move the z axis manually for 10mm, the axis moves for 10mm... so it seems to be configured right. I can't find the Solution :-( can anyone help?

Prusa I3
Marlin on Sanguinololu 1.3a
Hostsoftware: Cura, Pronterface, Repetier
Slicer: Skeinforge, Slic3r

Check your g code. What height is it instructing the printer to go go? Could be as simple as a slicer setting.

Hi,
the first lines of my gcode are:

;TYPE:CUSTOM
M92 E865.888000
M140 S70.000000
M109 T0 S220.000000
T0
M190 S70.000000
;Sliced /Users/Torben/Dropbox/Projekte/reprap/things/Twisted_Vase_Basic.stl at: Wed 29 May 2013 00:21:50
;Basic settings: Layer height: 0.3 Walls: 1 Fill: 0
;Print time: 0:41
;Filament used: 2.63m 22.46g
;Filament cost: Unknown
G21 ;metric values
G90 ;absolute positioning
M107 ;start with the fan off
G28 X0 Y0 ;move X/Y to min endstops
G28 Z0 ;move Z to min endstops
G1 Z15.0 F180 ;move the platform down 15mm
G92 E0 ;zero the extruded length
G1 F200 E3 ;extrude 3mm of feed stock
G92 E0 ;zero the extruded length again
G1 F9000
M117 Printing...
;LAYER:0
;TYPEKIRT
G1 X46.303 Y74.991 Z0.3 F9000.0
G1 X60.436 Y99.745 F1200.0 E0.6518
G1 X89.374 Y99.818 E1.3135
G1 X103.697 Y75.009 E1.9686
G1 X89.564 Y50.255 E2.6204
G1 X60.626 Y50.182 E3.2821
G1 X46.303 Y74.991 E3.9372
;TYPE:WALL-OUTER
G1 X62.686 Y53.615 F3600.0

As far as i understand it, it moves up 0.3mm

This looks to be OK. You move it up to 15mm then then down to 0.3. This should work.

I see the M117 commands. Do you use an LCD? If so, what is it reporting as the z height when you are printing?

Nope i'm not using an LCD could this disturb my printer? Is there something like a console in which i can see what the printer is doing ?

An LCD with Marlin firmware (and probably others as well) displays (among other things) the current head height. You can query the printer yourself by manually entering the M114 command. This will report out the current X, Y, Z, and E positions.

Oh,... when i home all axis, and send the M114 Command, it says "X:200.00Y:200.00Z:100.00E:0.00" so if it starts to print, and wants to move to 0, 0, 0 it moves all motors to the wrong direction, actually thats what happens with all 3 axis, where can i adjust this?

Problem solved :-) thanks for your help.

i just reinstalled the usb drivers arduino and the sanguinololu support, reflashed the firmware, now everything works fine :-)