security

Thanks for any help. I thought this would be the perfect place to ask my question.

My setup: Drupal 7.15 / IIS 7.5 / PHP5.3 / SQL Server 2008

I started receiving these crazy "Permission denied in drupal_unlink()" errors after an update from 7.13 to 7.14 (and then 7.15). At first, I focused on the permissions for the tmp directory. But after getting some assistance from Drupal's issue queue, I was able to pinpoint the problem as being related to the "sites/default/files" directory.