OK, I have to make some assumptions here, but I believe I have an answer for your question. I kinda wrote this so that any novices with the same problem could reasonably follow along.
Open Terminal
At the prompt, type:
diskutil list
A list of all the currently mounted local volumes should be listed. Find the Identifier of the FileVault user you cannot log into (should be labeled something like diskX where X is a number). Here's an example:
/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *160.0 GB disk0
1: EFI 209.7 MB disk0s1
2: Apple_HFS Macintosh HD 159.7 GB disk0s2
/dev/disk1
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *1.0 TB disk1
1: EFI 209.7 MB disk1s1
2: Apple_HFS Time Machine 376.5 GB disk1s2
3: Apple_HFS Media Disk HD 623.2 GB disk1s3
/dev/disk2
#: TYPE NAME SIZE IDENTIFIER
0: Apple_partition_scheme *319.4 GB disk2
1: Apple_partition_map 32.3 KB disk2s1
2: Apple_HFS main 319.4 GB disk2s2
In the example above, where it says Apple_HFS main, main is the FileVault user account that we're targeting. So the Identifier we want is disk2.
At the prompt, type:
diskutil unmountDisk diskX
Make sure you enter the appropriate number in place for the "X" for your situation. It may take a few moments, but the Terminal should return a message, stating:
Unmount of all volumes on diskX was successful
You should now be able to use FUS into that account again.
If that doesn't work, there's two alternatives I can think of: either restart your computer (not the most ideal solution); or kill the process keeping your sparsebundle open (could possibly result in data corruption):
At the Terminal prompt, type:
sudo lsof | grep sparsebundle
The system should return a list of open files that are being accessed by the process that's holding your FileVault image open. On Snow Leopard, it should be diskimages. Note the process id next to the name. Below is what mine looked like:
diskimage 68420 root 4u REG 14,2 8388608 5858242 /Users/main/main.sparsebundle/bands/241
diskimage 68420 root 5u REG 14,2 122880 5856490 /Users/main/main.sparsebundle/token
diskimage 68420 root 6r DIR 14,2 204 5856486 /Users/main/main.sparsebundle
diskimage 68420 root 7r DIR 14,2 56780 5856489 /Users/main/main.sparsebundle/bands
diskimage 68420 root 8u REG 14,2 8388608 5856497 /Users/main/main.sparsebundle/bands/0
At the prompt, type:
sudo kill [process id of diskimages]
(In the example above, my PID would be 68240.) You may have to repeat step 3 above, but that should allow you FUS into your account. However since you killed the diskimage process, it's possible that your disk image may suffer some corruption. (Note that I haven't tested this). I have been using FileVault on Tiger since May 2006 and on several occasions had to forcefully unmount my user account. But I haven't had any corruption problems with FileVault. But I don't have much experience on Snow Leopard's version of FileVault.
I also tried to see if I could unmount prior to logging out but it failed, probably because files were open as a result of me being logged in. I wouldn't doubt that you could write a script and have the system run it upon the final affected remote user being logged out, but unfortunately that's beyond my expertise.
One thing you can do is to remotely login as another user and do step 3 after you've ended your session until you're able to automate it. If you are able to find a way to automate it, please post it as I would love to learn how to do that.
AFP would likely be more Mac friendly. The other idea is that it's busy reclaiming space after you've logged out. How long do you wait between disconnecting on the network and trying to physically login? – Jeremy L – 2010-07-08T17:57:03.433
We have a mix of Mac, Linux, and Windows in the house (and until recently, the shared server was Linux), so rsync seemed nicely cross-platform and has worked for us for some time. Good suggestion on waiting, but that doesn't help -- remote logins (like ssh) correctly mount Filevault, but simply don't dismount when they are done. It's not a matter of waiting, it seems. – Larry Gritz – 2010-07-09T13:23:18.197