Compiled but won't run in Octoprint; returning code 255 when slicing files

[NovaViper]

--Edit-- I just realized I was using a bad installation of Slic3r instead of v1.39. for Slic3r PE Updating the issue to address the this.

I just finished installing Slic3r PE v 1.39 and I try to slice a file, but I get return 255 code with this error in the logs

2019-02-23 16:04:34,259 ### Slicing /home/pi/.octoprint/uploads/25mm_Laptop_Stand.tmp.1550937871860.stl to /tmp/tmp9PCj1T.gco using profile stored at /tmp/slicing-profile-temp-N8zKIm.profile
2019-02-23 16:04:35,805 stdout: => Processing triangulated mesh
2019-02-23 16:04:36,806 stdout: => Generating perimeters
2019-02-23 16:04:37,807 stdout: => Infilling layers
2019-02-23 16:04:38,809 stdout: => Preparing infill
2019-02-23 16:04:39,810 stdout: => Weight: 3684214611689463941774277197483813260663598020391977005176254612260859066056250662522645780909459766104356498067078003080939401240539444869332532052962127466747932431619058984550400.0g, Cost: 9821595203851300757189121493208296932783517341460360454460509347762578128081488657010417025567217746638588001437703000938288329926271916527439137480374293914864976708593984682074069349514166842717471911204221651148404713767832113220317908565733740118016.0
2019-02-23 16:04:40,025 stdout: => Generating skirt
2019-02-23 16:04:40,026 stderr: G-code export to /tmp/tmp9PCj1T.gco failed due to invalid custom G-code sections:
2019-02-23 16:04:40,027 stdout: => Exporting G-code to /tmp/tmp9PCj1T.gco
2019-02-23 16:04:40,027 stderr: 
2019-02-23 16:04:40,528 stderr: end_gcode
2019-02-23 16:04:40,529 stderr: 
2019-02-23 16:04:40,529 stderr: Please inspect the file /tmp/tmp9PCj1T.gco.tmp for error messages enclosed between
2019-02-23 16:04:40,529 stderr: !!!!! Failed to process the custom G-code template ...
2019-02-23 16:04:40,530 stderr: and
2019-02-23 16:04:40,530 stderr: !!!!! End of an error report for the custom G-code template ...
2019-02-23 16:04:40,531 ### Finished, returncode 255

How do I fix this error?

[NovaViper]

Ok, so, I discovered that for some strange reason, Slic3r PE 1.39.3 doesn't have the layer_z variable built in, so my gcode that keeps my printer from slamming into its z frame is what's causing the error. But this gcode is very essential. I've tried to update it but I've been given lots of headache over it, which I reported in issue #44.