I recall when you first open the Admin on a 64-bit box after install, MMC (The Microsoft Management Console, which Data Pump Admin runs in) gives you the choice for 64-bit or 32-bit MMC. You need to choose 32-bit.
Maybe you chose 64-bit.
If you have chosen or forced 64-bit, you can still change it by going into the Shortcut properties for the MDP Administrator and changing the shortcut target to:
"C:\Program Files (x86)\Monarch Data Pump\Datapump.msc" /32
(Include the quotes)
That will force MMC to work in 32-bit mode.