"vBulletin Database Error!" from time to time
 

Hello
I have VB software: forum, blog, advanced cms.
All software was closed for users (no one) because of content preparation & adjustment. But I recieve the messages like (see bellow) from time to time. What does it mean?
>>>>
Database error in vBulletin :
mysql_connect() [function.mysql-connect]: Can't create a new thread (errno 67); if you are not out of available memory, you can consult the manual for a possible OS-dependent bug /home/townblog/####/docs/forum/includes/class_core.php on line 311
MySQL Error :
Error Number :
Request Date : Wednesday, September 2nd 2009 @ 12:26:37 AM
Error Date : Wednesday, September 2nd 2009 @ 12:26:37 AM
Script : http://####/forum/calendar.php?c=1&week=1244937600&do=displayweek&mo nth=6
Referrer :
IP Address : ##.#.#.###
Username :
Classname : ##_database
MySQL Version :
>>>>>
I did not change the hosting adjustments since prof. installation of software.
Please, help me to understand
Thanks in advance.
Regards
nik