I own two of the Western Digital 2TB Elements (WDBAAU0020HBK) and have the same problem. The hard drives show up in Disk Utility, but that doesn't matter if they can't be accessed through Finder.
After unsuccessfully trying to scan and repair them I have been searching through the Western Digital Forums and it seems like Western Digital is well aware of the problem and currently working to fix the incompatibilities with Lion and their products. Since the operating system was recently released it is not officially supported just yet. We will need to wait until they release a compatibility patch. (Source)
I'm a little taken aback, that this is a known issue that hasn't been fixed before the release of Lion. Especially since it wasn't the first time Western Digital has experienced problems with a new Mac OS.
The source of the trouble is unknown to me but, it is known that apparently Apple has changed the AFP (Apple File Protocol), because they deemed it "not secure enough". (Source) This only concerns the NAS (Network Attached Storage) products of course, though there's most likely more changes to the file handling where that came from. So it's possibly up to Apple to come up with a solution.
Anyway, that's all I could find about this issue for now.