Reduced Disk Performance After SP1 WinXP

After installing SP1 for WinXP Pro, I now get a message that states, “Some files on this volume could not be defragmented”. I looked at the dfrag log for a list of what could not be defragmented and the list was blank. I noticed the performance of this hard drive has been reduced. When opening certain folders it now takes much longer to view the contents. I never experienced this problem prior to installing SP1. I have 2 physical hard drives in my computer C: & D: each having a single NTFS partition. My O/S & applications are installed on C: and D: is used only to store my personal files, documents, pictures, music, etc. Only my D: drive is having problems, C: is working fine.