unable to delete prefetch files by using C#.getting error

public Boolean CleanRecentData()
{
        isAllClean = true;
        String SysRecentPath = System.Environment.GetEnvironmentVariable("USERPROFILE") + "\\Recent";
        DirectoryInfo SysRecDir = new DirectoryInfo(SysRecentPath);
        File.SetAttributes(SysRecentPath, FileAttributes.Normal);

foreach (FileInfo fi in SysRecDir.GetFiles())   //Access Denied
                                                 //Exception is thrown here
        {
            try
            {
                fi.Delete();
            }
            catch (Exception ex)
            {
                recentLogLines.AppendLine(ex.Message);
                isAllClean = false;
            }
        }

        foreach (DirectoryInfo dir in SysRecDir.GetDirectories())
        {
            try
            {
                dir.Delete(true);
            }
            catch (Exception ex)
            {
                recentLogLines.AppendLine(ex.Message);
                isAllClean = false;
            }
        }

        return isAllClean;
    }