Juan,
I have been struggling with this as well. I have set up a Line Manager role in courses only, with permissions to read this, as well as a number of courses. The block does not show up on the front page.
However, if I change a single report to be visible by everyone, the block appears and the single report is visible.
If I change the role to be system wide, not just course, all reports are now visible.
I am running Moodle 2.3.1+ (20120712) and configurable reports v 2011040103.
This also seems to be the same as was reported on https://moodle.org/mod/forum/discuss.php?d=198542
Any ideas?
Cheers
Peter