Wow Bill....this is quite a sticky wicket.......
So, based on your info:
You can export an image to your desktop
You can export an image to a folder on your C drive
You cannot export an image to your external drive
You (apparently) can write files to your external drives because you have indicated that there are already files on there (I'm assuming that the files already on there were written there by you on this system you are using now?)
I wonder if the problem lies within the Export or simply accessing that drive from LR for whatever reason. I'm really with Rich on this one and would think that this is OS related and not a LR issue; however maybe we can further narrow it down.
In LR in the Library module in the "Folders" section on the left hand side, are your External drives showing up as "Green-Online"? Can you simply create a folder in the LR library module on your External drive? If you can, you know you at least have the rights to do so using LR as the creator of the folder. I would then try to use LR to copy a file to that newly created folder. Does that work? If it does, LR clearly can see the drive, and can write to it. This would point us toward a problem with the Export function.
I would agree with Rich that the drives *should* be transparent to LR; that is as long as they are functioning at the OS level, LR should simply be able to use them; no tricks involved.
See if the drives are showing up as available and online in the Library module and whether or not you can create a folder and copy files within LR. That should get us pointed in the right direction.
Cheers....
Todd in Chicago
QUOTE (Bill Wiley @ Nov 26 2008, 08:14 PM)

Yes, my computer has Vista as the OS. I installed it about 6 months ago and, to date, have had no problems.
Todd: I tried posting an image to both my 750gb My Book and an internal 250gb drive and neither worked. Got the same old message as before.
I just tried exporting a file to a test folder on my c:drive and it worked. That seemed like a miracle.
I don't know how to post a screen shot of the export box as it won't copy & paste.
Rich: There is enough space on both XHDs that I've tried, my 250gb has only 18gb used and and my 750gb still has 175 free.
I emptied the recycle bin, so that isn't the issue.
As far as permissions go, I checked Security on both XHDs and all permissions are checked. Surprisingly, I checked Security on my C:drive and a category called "Authenticated Users" was highlighted, but nothing was checked (this computer was originally set up with my wife's to share a printer, so that may be why the Authenticated Users was checked. I tried highlighting another category that shows all the boxes checked, but when I click okay, it doesn't hold. It always goes back to the Authenticated Users group. I don't know if this is a factor or not, as all my other programs have worked fine before and to the best of my knowledge (which may be limited), I've never had a permissions problem.
So I'm not sure what all that adds up to. I've tried setting the export box a variety of ways and always get the same "Export Failed"message.
Thanks for your thoughts. Even though they haven't panned out, it's given me more factors to eliminate.
Bill