You should have access on the server and the folder in which you would want to delete the files from.
Does your code above
string filePath = (sender as LinkButton).CommandArgument;
return the right path of the file?
It has to match the below
File.Delete(Server.MapPath("~/temp/") + newTempFile)
is the sub-folder within the root folder that has all the files to delete and
is the actual file name eg.