I started getting this really strange error while using a set of 3rd party controls & web parts from KWizCom (was working perfectly well on my dev box but stopped working on prod box):
Access to the path 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\template\layouts\KWizCom_WikiPlus\WPlibFiles\wkptmpl.aspx' is denied
1) Goto the corresponding folder under layouts (in my example KWizCom_WikiPlus), right click and then select Properties. Click on Security Tab and add the following accounts, namely NETWORK_SERVICE, WSS_ADMIN_WPG and WSS_RESTRICTED_WPG_V4 and give them "Full Control"
2) Click on "Advanced Settings" and Check Include inheritable permissions... and Replace all child objects permissions... and click OK
This should fix the "... access denied ..."