php ERR Can't get lock. Mailbox in use

I connected to mail server throw php and I had this error:

ERR Can't get lock. Mailbox in use

开发者_StackOverflow I can't get a new mail.

In php i use POP3 class.

How can I unlock it? I know that is a problem with IMAP and POP3. Thanks **

*UPDATE

PHP POP 3 mail class debug:

AUTH_SASL NOT PRESENT!

DISABLING METHOD DIGEST-MD5

DISABLING METHOD CRAM-MD5

S:+OK POP3 ns13.datateks.lv 2004.89 server ready

C: CAPA

S:+OK Capability list follows:

S:TOP

S:LOGIN-DELAY 180

S:UIDL

S:STLS

S:USER

S:SASL LOGIN

S:.

C: AUTH LOGIN

S:+ VXNlciBOYW1lAA==

C: YW5kcmVqcy5hbGVrc2VqZXZzQG5wZGNvbmNlcHQuY29t

S:+ UGFzc3dvcmQA

C: bnBkMjAzMA==

S:-ERR Can't get lock. Mailbox in use**

I don't think you can do anything in PHP to avoid this. Contact your mail server administrator to enable concurrent connections to a mailbox. If that is already enabled, increase the number of simultaneous connections allowed. Every mail server has different ways to achieve this.