Note: This documentation is for Moodle 2.7. For up-to-date documentation see error/tool installaddon/err curl exec.

error/tool installaddon/err curl exec

From MoodleDocs

This suggests problems with the validation of the SSL certificate of the remote (moodle.org) site. This is also a known problem in Moodle Windows 7 servers running the Moodle package for Windows. See SSL certificate for moodle.org for more info and possible solutions.