[Courier-imap] Fatal error: Cannot allocate memory when accessing a specific folder

[Nick D. <nd...@gm...>]

when I try to access a certain IMAP folder I get an error or no
response at all in all 4 clients I've tried (thunderbird v1.5, v2.0,
outlook express, Mutt)

In both versions of thunderbird I get the attached[1] lines in the
log. Here is the summary:
    2 OK LOGIN Ok.
    3 select "INBOX.Junk_according_to_TB"
    * BYE [ALERT] Fatal error: Cannot allocate memory
O.E. gives the very gentle message "Your IMAP server wishes to alert
you of the following: Fatal error:Cannot allocate memory"
Mutt it delays a lot then presents an empty folder

I also get the same error if I try to move a message in that folder

apt-cache showpkg courier-imap gives:
     Package: courier-imap Versions: 3.0.8-4sarge5

Any ideas or suggestions of what else I can do to diagnose and fix the problem?

__________________________________
[1] the relevant 8 log lines from thunderbirds log (I've removed some
reduntant text like the IP of the server and a standard prefix at the
begining of every line):
::NA:ProcessCurrentURL:       entering
::NA:ProcessCurrentURL:
imap://fetchuser@:143/select%3E.INBOX.Junk_according_to_TB:  =
currentUrl
     ReadNextLine [stream=8f7bca0 nb=233 needmore=0]
::NA:CreateNewLineFromSocket: * OK [CAPABILITY IMAP4rev1 UIDPLUS
CHILDREN NAMESPACE THREAD=ORDEREDSUBJECT THREAD=REFERENCES SORT QUOTA
IDLE ACL ACL2=UNION] Courier-IMAP ready. Copyright 1998-2004 Double
Precision, Inc.  See COPYING for distribution information.
::NA:SendData:                1 capability
     ReadNextLine [stream=8f7bca0 nb=122 needmore=0]
::NA:CreateNewLineFromSocket: * CAPABILITY IMAP4rev1 UIDPLUS CHILDREN
NAMESPACE THREAD=ORDEREDSUBJECT THREAD=REFERENCES SORT QUOTA IDLE ACL
ACL2=UNION
     ReadNextLine [stream=8f7bca0 nb=27 needmore=0]
::NA:CreateNewLineFromSocket: 1 OK CAPABILITY completed
::NA:SendData:                Logging suppressed for this command (it
probably contained authentication information)
     ReadNextLine [stream=8f7bca0 nb=16 needmore=0]
::NA:CreateNewLineFromSocket: 2 OK LOGIN Ok.
::A:SendData:                 3 select "INBOX.Junk_according_to_TB"
     ReadNextLine [stream=8f7bca0 nb=51 needmore=0]
::A:CreateNewLineFromSocket: * BYE [ALERT] Fatal error: Cannot allocate memory
::NA:TellThreadToDie:        close socket connection
     ImapThreadMainLoop leaving [this=a8f8190]