So now that I am using Ubuntu 18.04 and the latest Astrometry package, I am able to solved the two test pictures.
root@heidenrod-obs:/home# solve-field -z 2 -B none -P none -M none -S none -R none -U none -T -p -O NGC6910_300s_guided_2018-07-07.jpeg
Reading input file 1 of 1: "NGC6910_300s_guided_2018-07-07.jpeg"...
jpegtopnm: WRITING PGM FILE
Read file none: 1392 x 1040 pixels x 1 color(s); maxval 255
Using 8-bit output
Extracting sources...
Downsampling by 2...
simplexy: found 1158 sources.
Solving...
Reading file "./NGC6910_300s_guided_2018-07-07.axy"...
Field 1 did not solve (index index-4219.fits, field objects 1-10).
Field 1 did not solve (index index-4218.fits, field objects 1-10).
Field 1 did not solve (index index-4217.fits, field objects 1-10).
Field 1 did not solve (index index-4216.fits, field objects 1-10).
Field 1 did not solve (index index-4215.fits, field objects 1-10).
Field 1 did not solve (index index-4214.fits, field objects 1-10).
Field 1 did not solve (index index-4213.fits, field objects 1-10).
Field 1 did not solve (index index-4212.fits, field objects 1-10).
Field 1 did not solve (index index-4211.fits, field objects 1-10).
Field 1 did not solve (index index-4210.fits, field objects 1-10).
Field 1 did not solve (index index-4209.fits, field objects 1-10).
log-odds ratio 83.4399 (1.72784e+36), 16 match, 0 conflict, 42 distractors, 35 index.
RA,Dec = (305.785,40.7487), pixel scale 3.09452 arcsec/pix.
Hit/miss: Hit/miss: --+-++-+++-+
++++
+-+
+
+
+(best)
+
Field 1: solved with index index-4208.fits.
Field: NGC6910_300s_guided_2018-07-07.jpeg
Field center: (RA,Dec) = (305.785805, 40.748171) deg.
Field center: (RA H:M:S, Dec D:M:S) = (20:23:08.593, +40:44:53.416).
Field size: 71.7887 x 53.6359 arcminutes
Field rotation angle: up is -169.169 degrees E of N
Field parity: pos
Creating new FITS file "./NGC6910_300s_guided_2018-07-07.new"...
root@heidenrod-obs:/home#
and
root@heidenrod-obs:/home# solve-field -z 2 -B none -P none -M none -S none -R none -U none -T -p -O horizontal.jpg
Reading input file 1 of 1: "horizontal.jpg"...
jpegtopnm: WRITING PPM FILE
Read file stdin: 4016 x 2688 pixels x 1 color(s); maxval 255
Using 8-bit output
Extracting sources...
Downsampling by 2...
simplexy: found 1619 sources.
Solving...
Reading file "./horizontal.axy"...
Field 1 did not solve (index index-4219.fits, field objects 1-10).
Field 1 did not solve (index index-4218.fits, field objects 1-10).
Field 1 did not solve (index index-4217.fits, field objects 1-10).
Field 1 did not solve (index index-4216.fits, field objects 1-10).
Field 1 did not solve (index index-4215.fits, field objects 1-10).
Field 1 did not solve (index index-4214.fits, field objects 1-10).
Field 1 did not solve (index index-4213.fits, field objects 1-10).
======CUT======
Field 1 did not solve (index index-4218.fits, field objects 11-20).
Field 1 did not solve (index index-4217.fits, field objects 11-20).
Field 1 did not solve (index index-4216.fits, field objects 11-20).
Field 1 did not solve (index index-4215.fits, field objects 11-20).
log-odds ratio 434.831 (6.99361e+188), 87 match, 0 conflict, 245 distractors, 144 index.
RA,Dec = (18.2416,87.5421), pixel scale 17.4721 arcsec/pix.
Hit/miss: Hit/miss: +++-++++++--+-+++-++++++++++-++-+---+++++-+--+
++--+--+--+--+-+-+-++++-+--++
+---++++--+
Field 1: solved with index index-4214.fits.
Field: horizontal.jpg
Field center: (RA,Dec) = (18.165212, 87.543100) deg.
Field center: (RA H:M:S, Dec D:M:S) = (01:12:39.651, +87:32:35.158).
Field size: 19.299 x 12.9814 degrees
Field rotation angle: up is -80.0842 degrees E of N
Field parity: neg
Creating new FITS file "./horizontal.new"...
root@heidenrod-obs:/home#
I will obviously have to test it whenever I snap another picture and use the remote astrometry setup.