I've tried PerfectDisk and UltimateDefrag on my system and neither really makes much of a difference and I even find that PD slows my machine. I installed O&O Defrag and was very impressed with it's results - I noticed a speed difference. I set the program to ignore the ISR folder (same as PD). However, I get the common ckhdsk error when O&O scanes my C: drive. I've ran chkdsk with no errors. I've ran Spinrite - no errors. I've repaired my MBR (supposed to fix O&O's chkdsk error problem). I'm still getting the error. My question is: is FDISR interfering with O&O in some way? If there are no errors reported on my disk, then is FDISR the problem? Is it safe to ignore O&O's chkdsk warning and defrag my C: drive anyway? I know that PD complements FDISR, but I just don't like the way it defrags my system. When PD reports no fragmentation, O&O and UD report a high fragmentation on the same drives. Anyone else have a problem with O&O? I know the chkdsk problem is one that is often mentioned (Googling gives many, many results), but could it be that FDISR is interfering with O&O? Many thanks in advance, as always. Note: One factor that may be causing conflict is that I have installed Vista with FDISR and there have been many reboots, hangs and freezes since Vista installed. Although the Vista snapshot seems to be ok now, the installation was horrendous .