Go to Settings > Connect to PC > check on "Ask Me" and change the default connection type to charge only. Plug the usb cable into the phone and computer. On the phone pull down the notification bar and select type of connection you want. I usually select disk drive.
No problems for me with Win7 64 bit or WinXP 32 bit.
Have you also tried setting the default connection as disk drive and turn off the "ask me"?
If you have a card reader for the computer, you can always turn the phone off, take out the sd card, use an adapter if necessary, plug the card into the adapter and transfer the files. A pain I know, but it could be worth it.
If nothing else works, maybe try uninstalling the drivers on your computer, go to htc.com and find htc sync for the eris there. Sometimes the default windows drivers get in the way of the data transfer.