I have experienced this issue on a few occasions now so thought it was worth a mention.
Following best practices and creating accounts with least privileges in SharePoint may lead to an issue when you attempt to edit the SharePoint content source and my have an error displayed stating access is denied.
This is because the SharePoint Worker Process Group account (WSS_WPG) does not have permissions to the c:\windows\tasks folder.
To resolve this issue follow the article KB926959. The article does not state which server to apply this to so I would suggest applying this to all SharePoint servers in the farm – If anyone would like to feedback please comment. Also worth noting the WSS_WPG account is a local account and not a domain account.
Please note that on step 3 the command below may not work.
attrib –s %windir%\tasks
So before entering this command enter:
attrib +s %windir%\tasks
Then enter the first command again and that should work!
I’m not sure why this doesn’t work but I reported this to MS sometime ago.