When you set up your SSPs one of the things you will come across is Crawl Scheduling. This comes under Search Settings and allows you to configure Incremental Crawls and Full Crawls to the frequency you would like. For example, Full crawl once a day, Incremental Crawl every 5 minutes of each day.
I received an error whilst building a new farm this week when trying to set the Crawl Schedules.
ACCESS is DENIED. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))
To fix this you need to add the account WSS_WPG to the C:\Windows\Tasks folder on your Index server and apply modify rights.
If you cannot see the Security tab on the Tasks folder you need to open a command prompt and type is:
attrib -s %windir%\tasks
When you right click on the tasks folder having done this you should be able to see the Sharing & Security option.
To remove the option once you have applied the changes to the folder open command prompt again and type:
attrib +s %windir%\tasks