Often times you may need to grant the web server ‘Write’ or ‘Modify’ access to folders (for logging, loading files, creating graphics etc). The way to do that is to grant the required permissions at the folder level to the GROUP that the default IIS user belongs to.
The default built in GROUP under which the IIS process runs (in IIS 7) is IIS_IUSRS.
Bring up the properties of the folder (right click+properties). Click on the ‘Security tab':
If you do not have the IIS-IUSRS group in the ‘group or user names’ list, click on the ‘Edit’ button and then the ‘Add’ button. Type in iis_iusrs in the object name field and hit the “Check Names” button:
Then, make sure that the ‘Modify’ and ‘Write’ permissions for the IIS_IUSRS group is checked..Hit the ok button when done.