I am having a very similar issue using Moodle 2.7.3 - this is hosted with a moodle partner.
They had installed Progress Bar for us, and I tried it out on a few course pages and My Home, but then I saw the notice about switching to Completion Progress, so had them install it as well.
After adding removing instances of Progress bar, and adding Completion Progress and trying to go the the course page, I got a blank page with just the message: ""error reading from database". The same was true for the My Home page. Completion Progress is now removed and we are back to testing Progress Bar, but the newer block has some clear advantages for us.
Our host's support has offered no insight into what they think might be the issue.
Dale