Delayed Write Problem on $MFT and $Bitmap on an external hard disk

I put my VPC's on my external hard disk and run them off there, as the hard drive can run independently of Windows.

I've noticed over the past few months, that randomly, my external USB 2.0 hard drive (Freecom 400GB) disconnects for no reason and I get a balloon in the system tray with the title "Delayed Write Problem" , then something to do with G:\$MFT or G:\$Bitmap.

Yesterday, I was defragmenting my external hard disk and noticed it kept happening. I turned it off and on again, started defragmenting and the same problem happened.

I thought it might be the writing caching, which helps improve performance, so when viewing the properties of the drive (My Computer -> [External Hard Disk] -> Right-click Properties -> Hardware -> Properties -> "Enable write caching on the disk"), I turned this option off.

Another defragmentation session and the same problem happened again and again.

What I finally realised was that I was using some software (DAEMON Tools Lite) for mounting ISO's to a CD drive. Although the software wasn't running, I still had the CD drive present in my drive listing. I loaded up DAEMON Tools Lite and turned off the emulated CD drive (which I wasn't using anyway) and HEY PRESTO! it was working.

I defragmented half the drive and then turned write caching back on and it was fine!

Hope this helps someone, as when a hard drive disconnects and a VPC is running off it, you are in trouble!