Lightroom :: 3.6 Can't Export To Directory On READYNAS

I have Lightroom 3.6.  I also have a lot of images.  So I got a READYNAS RNDU4000 disk array (RAID) with 4 disks each of 2 TB. My computer is running Windows XP Professional SP3.  It mounts the RAID array as a network drive just fine.  Now suppose I have some new images.  I make a new folder on the RAID array, lets say it is called "WildAnimalPark" and copy the images in there.   I start up Lightroom, and choose Import Files, and point it at WildAniamalPark, and it imports the images just fine, and lets me make adjustments.  (The Lightroom catalog is in my F drive, a hard drive on my computer.)  Now I want to export smaller jpegs suitable for web or e-mail.  So I go to File->Export.  I tell it to export the images to "Same folder as original photo", and check "Put in Subfolder" and name the subfolder "email".  Farther down I ask for the images to be scaled to 800 pixels on the long edge and to limit the file size to 125K.  (I doubt these details matter.)  When I click "export", it appears like it is going to work.  You can see the progress bar move across as it makes the files.   But then I get an dialog box that says, "Some export operations were not performed.  The file could not be written," followed by a list of off the files it should have written.  When I look it the original directory, I see that it has created the subfolder "email" (so it really can write to the RAID array), but it is empty. 

I should add that it works perfectly if I put the directory on a local hard drive.