If you receive an “access denied” message on your PC, whether in Windows or Linux, which occurs when trying to delete or modify a file, it can usually be narrowed down to a few reasons:

– The file is marked as readonly
– The file is located on a CD, disk, drive, removable device or any other storage type which is either marked as readonly for the entire volume or your files are contained within a readonly partition in this volume (which can easily occur in linux if you manually mount a drive improperly)
– You do not have access to delete the file or are not an owner of the file
– The file is currently open or in use

If you are deleting the file using code in your .Net application, be sure to remove the “read only” attribute which won’t prevent a user from deleting it, but will definitely halt your application. (code reference).

If you are absolutely sure you should be able to delete the file, or are trying to remove a file which be malicious or difficult to delete, there are tools available such as file assassin which can be used to override the normal OS safeguards (if you have the right know how and permissions) and delete the file anyway.

References
Imran Akram (WordPress BLOG)http://imak47.wordpress.com/2009/01/15/how-to-remove-readonly-attribute-from-a-file/
MalwareBytes “FileAssassin”, http://www.malwarebytes.org/fileassassin.php