big props to these folks at companionlink.com:
http://www.companionlink.com/support/kb/Droid_Pro_(some_Motorola_phones)_do_not_mount_after_Android_Update
I had the same issues and found their resolution worked perfectly, Verizon's article was useless... Thanks.
Droid Pro (some Motorola phones) do not mount after Android Update
On October 15, 2011 Motorola pushed out an Android 2.3.3 update to Droid Pro users that caused their devices to no longer mount in USB Mass Storage Mode. When connecting the device in Mass Storage Mode, then PC tries to install an MTP device driver.
Since CompanionLink and DejaOffice utilize USB Mass Storage Mode for USB sync, this prevented DejaOffice and CompanionLink from syncing via USB.
The problem is a driver conflict on the PC that can be resolved by following the steps below.
1. Connect the Droid Pro to the PC, pull down the notification bar, select USB Connection, then USB Mass Storage and wait for the MTP device driver to fail to install
2. Open Device Manager and look under "Portable Devices" for an "MTP USB Device" (or driver letter) with a yellow warning symbol
3. Right click MTP USB Device and select "Update Driver Sofware..."
4. Do not select "Search Automatically..." and Select "Browse my computer..."
5. Select "Let me pick..."
6. Do not select "MTP USB Device" and Select "USB Mass Storage Device" then Next, then Close.
