Solved: Moodle – Coding error detected, it must be fixed by a programmer: Failed to unserialise data from file. Either failed to read, or failed to write

Problem:
There was a file locked by cache store system.

Solutions:

1. Execute script purgecaches to reset the cache system. your_site/admin/purge_caches.php
2. Remove all files and directories under the directory /moodledata/cache

Note: It is always safe to rename the directory and create an empty one with the same name (cache). If you like, Number 2 has been more useful for me in the past.