I got the same error on my Synology NAS (DSM 6.2), with Web Station, nginx, PHP 7.4 (no PEAR) even with the latest version of MantisBT (2.25.2).
Since my project administration depends on Mantis, I decided to track down the error, and I think I found a bug in ado-php.
1. index.php line 31 requires core.php
2. core.php line 269 requires API database_api.php
3. core/database_api.php line 154 ADONewConnection::Connect is called
4. vendor/adodb/adodb-php line 695 ADONewConnection::_connect is called
The problem: the function ADONewConnection::_connect() does not exist (!), probably some autoloader is activated which obviously can not find the file and triggers the error. Although I don't see why the same code worked perfectly on my Debian 11 server?
I've missed the fact that ADOConnection is an abstract class.. my bad.
I did however solve the problem (after more than 2 hours, because of the initial unhelpful error message)
- Changing the configuration parameter from 'localhost' to '127.0.0.1' changed the error to 'Connection refused'
- After enabling TCP/IP on port 3306 in DSM -> Package Manager -> MariaDB 10 -> Open, the database connection worked