This was previously a question but I have it sorted out now and I can now transfer files between my Droid X and my PC via Media Share and USB.
You have to follow the steps exactly and do not connect via USB until you get to that step that tells you to. If you connect the USB cable before going through the Media Share process then you will get SD card errors. Here's what I did -
1 - Open Media Share
2- Press "Start"
3 - Select "Computer"
4 - Select "copy"
5 - Select "USB"
6 - "Next"
7 - NOW connect the cable. You should get a message about connecting with USB mass storage
8 - "Next"
9 - Enable Memory Manager for "USB Mass Storage" if not enabled
10 - Open Windows file manager on PC
11 - "Next"
12 - In Windows, Drag and drop content between PC and phone
13 - Files will now copy
14 - Done!
Eventually I will be doing file transfers either by W-Fi or Bluetooth after I figure those out. And hopefully Verizon will release a 64 bit VCast manager.