Today I’ve installed Mantis 2.13.1 in my Debian 9. When the install process ended this error appeared:
APPLICATION ERROR #2900 For security reasons MantisBT will not operate when $g_crypto_master_salt is not specified correctly in config_inc.php or is shorter than 16 characters long. Please use the «Back» button in your web browser to return to the previous page. There you can correct whatever problems were identified in this error or select another action. You can also click an option from the menu bar to go directly to a new section.
Which was easily solved by copying config/config_inc.php into the mantis ‘root/main‘ folder (upper level).
After doing this and reloading the page two warnings appeared:
Warning: «admin» directory should be removed, or access to it restricted.
Warning: You should disable the default ‘administrator’ account or change its password
Once I’ve solved both errors everything worked fine.