Hi guys...I don't know if anyone is still having this issue, but here's what I did (and it appears to have worked, so far):
First of all, my Curve 8310 was nuked when I tried upgrading from v4.2 to v4.5, after just having installed DM v4.7.
Go
here, and download and install (to your PC) DM v4.6.
Next, go
here and download and install (to your PC) the OS for your provider.
Next, follow
this guide. When it comes to step 2, if you have problems with the device connecting here's what I did:
-Remove the battery from your BB
-Click Next to go to the connection screen
-Hover your mouse over the Next button and have your hand ready, and with your other hand plug the other end of your USB data cable into your BB
-As soon as you see the textbox switch to "USB-PIN:UNKNOWN", click Next
Now, here seems to be the part where a lot of people have issues (myself included):
Once you select the apps you want to install with the OS, you'll see a progress bar completing several steps.
Replace the battery in your BB (put it back in) while the progress bar is at the very first stage, it says something like "Erasing old information" or "Erasing old data", or something along those lines.
Once you replace the battery at this time, you should
NOT receive the "Unable to complete the loading operation - Unable to reconnect to the device during a multi-stage load operation" error message, and the process should complete successfully.
After that, your BB should reboot (if you keep using the guide I posted above, it will tell you that the reboot can take about 10-15 minutes, so don't worry when it doesn't come back right away).
Hopefully by the time it reboots your BB will be back with your new OS, and working properly.
These steps worked for me on a 8310 Curve. Hopefully they will work for you as well.
I did a lot of research, and read a lot of other forum posts to finally solve this problem. You can find my original help post
here. Credit to those who helped me out, and who pointed me in the right direction. I hope this post helps anyone else who runs into this problem in the future to revive their BB!