drush pm-update of 6.27 to 6.28 yields this error: Allowed memory size of 67108864 bytes Possible Duplicate:
  “Allowed memory size” errors on common tasks  




we put our site into maintenance mode, 
temporariliy removed some symbolic links that have confused drush in the past,
and tried to do this:
[~/drupal-6.25]# drush pm-update

where we got this error:

Refreshing update status information ...

Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 199690 bytes) in /home/kettles/drupal-6.25/modules/update/update.module on line 549
Drush command terminated abnormally due to an unrecoverable error.   [error]
Error: Allowed memory size of 67108864 bytes exhausted (tried to
allocate 199690 bytes) in
/home/kettles/drupal-6.25/modules/update/update.module, line 549
[~/drupal-6.25]#

The directory is called drupal-6.25 but really holds a 6.27 install.

Thanks,
See this thread.

What you need to do basically is to increase the memory in your php.ini file. Start with 128M and if you are still getting that error, try with more.