I've been having a problem with Wordpress and it seems to be caused by wincache. Several others have reported the same problem on the Wordpress.com forums
Essentially what happens is when attempting to upgrade a Wordpress plugin, the upgrade fails with a message similar to this -
Unpacking the update.
Installing the latest version.
Deactivating the plugin.
Removing the old version of the plugin.
Could not create directory. DIRECTORY\wwwroot/wp-content/plugins/akismet/
Plugin upgrade Failed.
I'm running Wordpress 2.9.2 on a Windows 2008R2 VPS, with PHP 5.2.13 and wincache 1.1
Checking on the VPS, the plugin directory is there but inaccessible even as an administrator, with "access is denied". Restarting IIS results in the folder disappearing. The plugin can then be installed.
Clearly there's some locking problem occurring somewhere. Disabling wincache stops the problem.