Problems running tarsnap-keygen

[James Montgomerie <jamie@th.ingsmadeoutofotherthin.gs>]

I hope I'm not missing something obvious here...

I'm trying to set up Tarsnap on my shared web hosting account (I plan  
to use it to make daily backups), but I can't get tarsnap-keygen to  
work.  I don't have root access, I'm doing everything in my user  
account.  Tarsnap is configured with --prefix=$HOME/admin, and my  
$PATH is set up appropriately to find stuff installed in ~/admin/bin.

Here's what happens when I run tarsnap-keygen:

[~/admin] things$ tarsnap-keygen --keyfile ./tarsnap.key --user jamie@th.ingsmadeoutofotherthin.gs 
 --machine th.ingsmadeoutofotherthin.gs
Enter tarsnap account password:  < I enter the correct password here,  
as set up on www.tarsnap.com >
tarsnap-keygen: error in AES_set_encrypt_key
tarsnap-keygen: error in AES_set_encrypt_key
tarsnap-keygen: Too many network failures
tarsnap-keygen: Error registering with server

The server is running Solaris:

[~/admin] things$ uname -a
SunOS 5.11 snv_67 i86pc i386 i86pc

Hope someone can provide some ideas!
Jamie.