Power Rout / G-Code problem

[Karten Products]

Hi All - 
This is my first post in the forum, so I'll do a quick intro and background then try to describe my current problem concisely hoping someone can help me!

I bought an M3 last fall for my intro to CNC Routing - LOVED it! ..and quickly outgrew it.  Just bought a Power Rout and have been having moderate success (created a nesting fixture, and a vacuum boot so far).  

Here's the issue:
Computer is up with Universal G-Code Sender (latest version) and connected to PR.
PR is homed, and then I go to zero out my work piece.  Still no issues here.  To set zero I either click the X- Y- or Z- zero buttons in UGS, or type the command: G10 L10 P1 X0 Y0 Z0
I load my program which the first 20 lines are copied below.  I don't get past line 14 before I have to pause the script or E-stop the machine!  The problem that forces me to pause the machine is listed after the code.    I have comments for some lines in [] below for the purposes of this question - they aren't in the G-code.

%
(T100001 - fixture)   [comment line]
(Tie down points program 1) [comment line]
(T1 D=0.25 CR=0 - ZMIN=-0.75 - flat end mill) [comment line]
G90 G94
G17
G20 [" units.  That's fine - the design is in " units]
G28 G91 Z0.1   [trying to tell it to go up 0.1" from Z0. I think this is the line that causes trouble?? This seems to work in other files.]
G90

(Bore1)
M9
T1
S15000 M3
G0 Z0.1 [changed this line per one of Derek's you tube videos from G54]
G0 X23.0625 Y22.975
Z0.6
Z-0.02
G1 Z-0.075 F40
G18 G2 X23.0875 Z-0.1 I0.025


Problem: As soon as I hit the play button in UGS, the first thing the PR does is go in the Z direction - past the homing switch! - until it bottoms out on the Z-motor bracket.  I have no idea why it's doing this with the above command sequence.  Please help?
Thanks,
Jeff

[Derek the Admin]

The G28 position isn’t set with G28.1 so it will not move to a predictable position when it sees that F28 command.

[Derek the Admin]

Also, try to make that a z0 instead of z0.1 in there on the g28 line.

I have a video in the video tutorial sticky post about homing and home (G28 and G30) positions that may be useful to you.

[Karten Products]

I was actually thinking that maybe I hadn't set the G28.1 yet as I was driving to dinner. I commented the line out with () and it ran fine. Will take another look at your homing videos too! Thanks for quick response.
So, in the G-Code, assuming I've put my router bit at x,y,z-0, I can enter G28.1 the line before the G28 line to "home" G28, and then it will be predictable, correct?