I just launched a new Testlink instance but I was not able to reproduce the issue.
adodb-.inc.php is a weird name for a file. I think that there should be something else after the dash (
-) but for some reason Teslink does not know what should be and so is not able to find the file.
Inside /opt/bitnami/apps/testlink/htdocs/thirdparty/adodb/drivers/_ there are a lot of database drivers so maybe there is an issue with the database configuration.
Can you check the content of the file /opt/bitnami/apps/testlink/htdocs/configdb.inc.php_ ?
It should contain something like this: