[Captivate Q&A, Help & Troubleshooting] xwiljar:
I came up with this a while back. Could very well be the same issue.

Let me start by saying I'm flash happy, and everyone that knows me personally, tells me to just quit jacking with my phone. NOT A CHANCE! I'm on my 3rd Cappy and shouldn't have ever exchange it again. I only had to in the beginning, because I was a newbie and had not know enough, but to get me in trouble.

I presume that this should work on all Windows OS's. I personally am running Vista Enterprise x86.

My symptoms:

Plug in phone to the usb and it there was about a 15% chance off being able to mount to usb, and Windows recognizing as a mass storage device. I tried un-installing drivers and re-installing and it would work some of the time, until the point came when parts of the driver install would fail. Then to the point when it was just completely unrecognizable. I thought I had it fixed because it seemed intermittent. In the middle of flashing to stock, something interrupted communication between the pc and my phone. Restarted the phone and attempted the flash again. Got a little farther and froze again. I had to use another pc that I had never connected my phone to before and I was able to use my jig to trigger download mode, because no buttons combinations would allow it into download mode.

This got me thinking that it was specific to my pc and not my cable or my phone.

My resolution:

I went straight to the registry and went to find. I deleted every entry that came up for "i897" and "i9000" excluding what was listed in the system volume information, as I didn't have permissions to remove any keys. I didn't keep count, but I probably deleted 300-400 registry keys that pointed to my phone. It seems as if with each developers rom that I had flashed, there was an entry for a different device. Don't quote me on that, because it is just my personal consensus. I also un-installed the samsung drivers, the unknown device driver, kies software, and anything associated with samsung. I noticed that next to all of the i9000 instances, the hex key for me started with 1000ee. So I also searched for the first part of that key trying to ensure that all instances of the device. Lastly, I deleted the samsung folder from program files.

I installed the samsung drivers package commonly listed in all of the other threads for x86 operating systems. I plugged in my phone and watched as each and every driver installed successfully. Keep in mind different drivers are installed depending on if you have usb debugging on/off, and the options for if the preferences on you phone are set to media, storage, or kies. I have multiple usb ports, however testing has shown me that, for me and my setup, I can plug into the port that I used when installing the drivers the final time, I am able to connect consistently. Earlier today, I tried to plug into a different usb port and it was an unknown device. I am led to believe, this is because I didn't un-install the unknown device on this particular port.

If you intend to work in the registry, please remember to always back it up first. You can always restore.

Hopefully my findings can help you as they did me. Happy flashing and I would like to thank the community for the dedication to assisting each other and the developers, for making flashing, better than crack cocaine. Flashing rom's doesn't make you twitch near as much as a crackhead.