Errors when ad file cache enabled

Hi,

I'm getting persistent errors reported in the Ad admin pages and also when attempting to flush Drupal caches:

# The selected file C:\Development\acquia-drupal-site\acquia-drupal\temp\fil4987.tmp could not be copied.
# The selected file C:\Development\acquia-drupal-site\acquia-drupal\temp\fil4998.tmp could not be copied.
# The selected file C:\Development\acquia-drupal-site\acquia-drupal\temp\fil49A8.tmp could not be copied

I have my file cache setting setup to use 3 files, so I guess these are the file being used. The errors do not appear in Watchdog, just in the UI.

Disabling the file cache component fixes the errors, so I guess there is a config issue?

Any ideas?

Thanks