Depending on what you actually do, several different errors may occurs. E.g., when entering your Inbox/Outbox/Sentbox:

[phpBB Debug] PHP Notice: in file /includes/functions_privmsgs.php on line 1105: Undefined variable: return
[phpBB Debug] PHP Notice: in file /includes/functions_privmsgs.php on line 1105: Undefined variable: return
[phpBB Debug] PHP Notice: in file /includes/functions_privmsgs.php on line 1105: Undefined variable: return
[phpBB Debug] PHP Notice: in file /includes/functions.php on line 2618: Cannot modify header information - headers already sent by (output started at /includes/functions.php:2190)
[phpBB Debug] PHP Notice: in file /includes/functions.php on line 2619: Cannot modify header information - headers already sent by (output started at /includes/functions.php:2190)
[phpBB Debug] PHP Notice: in file /includes/functions.php on line 2620: Cannot modify header information - headers already sent by (output started at /includes/functions.php:2190)

When viewing a sent PM or new PM in your Inbox:

[phpBB Debug] PHP Notice: in file /includes/functions_privmsgs.php on line 1105: Undefined variable: return
[phpBB Debug] PHP Notice: in file /includes/functions_privmsgs.php on line 1105: Undefined variable: return
[phpBB Debug] PHP Notice: in file /includes/functions_privmsgs.php on line 1105: Undefined variable: return
[phpBB Debug] PHP Notice: in file /includes/ucp/ucp_pm_viewmessage.php on line 204: Undefined index: email_pm
[phpBB Debug] PHP Notice: in file /includes/functions.php on line 2618: Cannot modify header information - headers already sent by (output started at /includes/functions.php:2190)
[phpBB Debug] PHP Notice: in file /includes/functions.php on line 2619: Cannot modify header information - headers already sent by (output started at /includes/functions.php:2190)
[phpBB Debug] PHP Notice: in file /includes/functions.php on line 2620: Cannot modify header information - headers already sent by (output started at /includes/functions.php:2190)

However, Composing / Drafts and Options in this subsection work fine. Obviously, only displaying the contents of boxes and the PMs theirselfes is messed up.

Used current CVS for this time.