Access denied error in AIF file adapter

‘AIFGatewayReceiveService’ is encountering the following error.

“The file system adapter is unable to read the file C:\FTPRoot\input\aFile.xml. Error: Access to the path ‘C:\FTPRoot\input\aFile.xml’ is denied.”

Document owner is the same as the logged in user. And i have assigned FULL CONTROL to it on input directory. What is the reason here.

I granted AOS (the account the aos is running on) full rights and the problem is fixed.