In SSRS 2008 , If you right click the file folders under the Installation Folder.
open the property window of the folder . check the security tab . and you will find there is a special user add in the account list.
please see below.
This user is used to access the SSRS. so if you check the logfiles folder's user list . you can find this user is granted read/write privilege so that SSRS can read and write log under this folder . I think if you want to add some custom feature to SSRS . like modify some files in SSRS .
You must grant right enough privileges to this special user .
In my case . I add my log file under the "Program Files\Microsoft SQL Server\MSRS10.MSSQLSERVER\Reporting Services\ReportServer\" folder
and I create a folder name "System\Log" in it .
After that . my custom log file was created .
otherwise. you will got a exception in the SSRS Log file (which is located in Program Files\Microsoft SQL Server\MSRS10.MSSQLSERVER\Reporting Services\LogFiles)
"system.unauthorizedaccessexception access to the path is denied"
Does it make sense to you ?