Windows cannot access the external harddisk partition not responding

The problem I describe above appears to have been associated with, if not directly caused by, the contents of a couple of registry keys used by both Acronis Disk Director (Version 10.0 for which I paid) and Acronis True Image WD Edition (Version 11.0, which was free) which I had installed.

A big clue came from this Microsoft Support article http://support.microsoft.com/kb/925196 which, under the "Let me fix it myself" subtitle, describes certain registry keys which if corrupt can cause hard drives to be unseen. Looking at these registry keys I found they contained the snapman driver, which Google revealed to be an Acronis product. This tied in with my Acronis observation mentioned in my question and the driver details visible under Device Manager->disk drives->(the disk in question)->Properties->Driver->Driver Details which showed snapman.sys as one of the drivers. I therefore deleted the registry keys as recommended by the Microsoft article (actually only the UpperFilters, I didn't have a LowerFilters), and also removed the snapman entry from the other keys in which it appeared following this Acronis Knowledge Base article http://kb.acronis.com/content/1620 Figuring this probably broke my Acronis products I then uninstalled both of them using Control Panel->Add or Remove Programs. With all of these steps completed my drive attachment/removal problem was fixed : I successfully attached a FAT32 mass storage device and safely removed it four times in a row. I then reinstalled Acronis Disk Director (the Complete program, for All Users) which put the snapman driver references back into the registry keys. Then I successfully attached and safely removed the same FAT32 mass storage device another three times. I've decided not to risk reinstalling Acronis True Image. I suspect it may install its own version of the snapman driver, which may conflict with Disk Director's, and make further changes to the registry keys. It can be run from a bootable disk, and since I only run it occasionally that's good enough for me.

I say associated rather than caused above because I'm pretty sure I had both Acronis products installed and was running them off and on for many months without any drive attachment/removal problems. While trying to solve this problem I Googled the search term '"is not accessible" "the parameter is incorrect"' without the single quotes and read the first 50 web pages returned. A theme that cropped up a few times was people facing this problem after having changed drive letters. This was interesting because I suspect that my own problem dates back to last July or so when I was repartitioning and changing drive letters on my backup drives. I was doing this using Acronis Disk Director. So I speculate that changing drive letters may somehow be involved in triggering this problem. This is speculation, but it does suggest another solution to the problem which might work, perhaps even for people who are not running Acronis, which is to do a system restore to the day before you were changing drive letters. I tried to do this myself before I zeroed in on the registry keys, but unfortunately my backups/restore points didn't go back far enough.

EDIT : I find I still have a problem with my machine's inbuilt card reader. When I insert an SDHC card (formatted FAT32) I can see it properly, but I cannot safely remove it. However, if I use a $2 card reader to turn the SDHC card into a USB drive then it attaches and safely removes without a problem.