I have seperate catalogs on each of my e-sate external drives -- no problem. However, some projects we have here need access by both my computer and my wife's (AD/graphic designer). For that reason, certain jobs are kept on the network drive for easier access.
If you are running Windows, there is a 'fix' for this - it isn't very nice, but it does work!
You need to use the Windows (actually DOS) 'subst' command to create a virtual drive, with a new drive letter, for the network drive - this fools LR into thinking that it is a local drive. (Anyone, like me, who worked with MS-DOS before all this graphical nonsense came along, should remember the DOS command prompts!).
The command has to be run in a DOS window, or from the autoexec.bat file. I have shortcut on my desktop that does it - it is called 'Create Virtual drive T:', and looks like this:
If you want to put it in the autoexec.bat file (which lives in root folder of the boot drive), then find and open the file in a text editor of your choice, and add the line:
subst t: s:\
Putting this line in the autoexec will cause the virtual drive to be created each time the system is started
The network drive has previously been assigned the drive letter s:, and the new virtual drive now has the drive letter t:. It appears in Explorer as 'Disconnected Network Drive (T:)', and can be accessed from LR's 'Select Catalog' startup dialog. You can then select any LR catalogs on the drive in the usual way, and they will open without error - note that LR will be quite a lot slower than you're used to, as it reading and writing to over a network, and, of course, don't attempt to access the same catalog from different machines simultaneously!
I'm not familiar with the Mac, and have no idea if there is a similar function available.
I use this technique so that we can access family and holiday shots and similar from my wife's laptop in the comfort of our living room, rather than having to drag visitors into the hell that is my study/digital darkroom!!
I hope this works for you
Visit www.stevemortonphotography.co.uk for some photo's of North Devon landscapes and gardens.
PS. I have just noticed that a much more detailed description of this trick has been published in the LR forums here:http://www.lightroomforums.net/showthread.php?t=1595
You'd probably better take note of Adobe's warnings as well, although it has worked fine for me.