AstroPi3 Part 1 - Raspberry Pi 3 as a autoguider computer
AstroPi3 Part 2 - Creating the Installation Image
AstroPi3 Part 3 - Installing Ubuntu Mate
AstroPi3 Part 4 - Installing AstroPI3
AstroPi3 Part 5 - PhD2 Configuration
AstroPi3 Part 6 - DSLR/Guide Camera Setup and Control
AstroPi3 Part 7 - Raspberry Control with Tablet/Cell
AstroPi3 Appendix A - Index of Possible Problems, Causes and Solutions

Here is a list of possible problems that may occur during installation. This list will be updated as feedback is received from people who have followed the tutorial.

1. Raspberry does not start or has never started even with the card containing the Ubuntu installation.

Color screen or black screen

Possible causes:
a) The raspberry model is not compatible with the current version of Ubuntu Mate.
At the time of writing only Raspberry Pi 3, and not later models like Raspberry Pi 3b+ are supported in version 16.04.2 (Xenial).

a) Wait for a new version of Ubuntu that is compatible with Raspberry Pi 3b+
b) Purchase the Raspberry Pi 3.

2. Ubuntu blocks booting during initialization and at the end it shows a message like " ubuntu unable to mount root fs on unknown-block" ...

Possible causes:
a) The SD card partition is damaged
b) The SD card has been damaged due to poor quality.

Format the card and reinstall the ubuntu image, and redo the installation process. If the problem still occurs, the SD card is of poor quality and needs to be replaced with a more reliable brand.