I have had a lot of problems due to a "Error Drive D:", that caused an anoying CHKDSK every time I started W7. This forced to me to modify the register in the way explained by several posts in these threads, but the problem is always there and this caused failures in backup and in defragmentation.I do not know the reason, but I have found that this was caused by IE8, after navigation by some webs. So, does not matter that you perform a CHKDSK at startup, because as soon as you navigate with IE8, dirty bit appears again. After more investigation I found that the folder "Temporary Internet files" was moved to the drive (partition) D:. I returned to its default location in C: \Users ... and bingo! ... the disk error disappeared. To be sure about that, I moved again the IE8 temporary Internet files to D:, and immediatly I had again the "dirty bit" problem and all the involved problems. So, solution: "Internet temporary files" has to be located in their default location. Sorry again about my bad English and I hope it will be helpfull for all of you.