Hi federica.
Filling in the "Keywords" field in "Author Manager" causes the error "0 Class "str_ireplace" not found".
Thanks for reporting.
I fixed the bug. I will publish the new release as soon as possible.
If you want to fix it immediately, open administrator/components/com_abook/tables/author.php
then change line 50
from
$after_clean = str_ireplace::str_ireplace($bad_characters, "", $this->metakey); // remove bad charactersto
$after_clean = StringHelper::str_ireplace($bad_characters, "", $this->metakey); // remove bad characters
Now the error does not occur. Thank you very much.