As I wrote above this situation is really bizarre. RadAsyncUpload send the files do tempFolder "~App_Data\RadUploadTemp" but it cant move the file to target directory.
My target folder has full permissions to everyone. So I decided to try a different approach to test. I chaged the property "temporary folder", instead of "~App_Data\RadUploadTemp" I wrote "~/documents/files" which is my target folder. Surprise, It works! RadAsyncUpload is able to upload a file to this target directory so why it throws "access denied" when it moves the file from default temporary folder? It doesnt make any sense!
I decided to put the temporary folder equal to my target folder and now it is woriking as expected.It uploads the file with a random name than it changes the file name to its original name. The difference here is that It's not moving the file to another directory
I will keep it this way and move on cause I lost almost a day with this issue but I would like to hear from Telerik what they think about this issue.