I got the following error while trying to upgrade a site feature in SharePoint:

The copying of this file failed: Feature.xml. 
Access to the path 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\
Template\Features\<MyFeature>\Feature.xml' is denied.

I hadn’t changed any of the SP settings and the process for doing the deployment hadn’t changed so what was SP getting upset about now??? Taking a look at the directory where the Feature.xml was supposed to be installed provided me with the answer. For some reason, yet to be explained by computer science, the directory was left in a state of limbo. I couldn’t open it to view the content, see the security settings or rename/delete it. First of all I tried resetting IIS to see if that would release its grip on this defunct directory but this gave me no further progress. In the end I restarted the machine, the phantom directory disappeared and I was able to continue on with my deployment process as normal.