> There's no firewall between the client and server. In fact, the
> client and backup tapeserver are one and the same in this problem.

OK, so that rules out connection problems.  Can you check the timeout
values?  I'm sorry I'm probably asking for information that you already
gave; but do you have a /tmp/amanda/sendsize.<date>.debug to analyse? 
Here's how mine looks (on the server machine):
---
sendsize: debug 1 pid 1043800 ruid 0 euid 0 start time Wed Apr 16
00:45:09 2003
/usr/freeware/libexec/sendsize: version 2.4.2p2
calculating for amname '/etc', dirname '/etc'
sendsize: getting size via gnutar for /etc level 0
sendsize: missing exclude list file "/etc/amanda-exclude.gtar" discarded
sendsize: spawning /usr/freeware/libexec/runtar in pipeline
sendsize: argument list: /usr/freeware/bin/tar --create --file /dev/null
--direc
tory /etc --one-file-system --listed-incremental
/var/amanda/gnutar-lists/pac_et
c_0.new --sparse --ignore-failed-read --totals .
Total bytes written: 819200 (800kB, 620kB/s)
.....
sendsize: getting size via gnutar for /etc level 1
sendsize: missing exclude list file "/etc/amanda-exclude.gtar" discarded
sendsize: spawning /usr/freeware/libexec/runtar in pipeline
sendsize: argument list: /usr/freeware/bin/tar --create --file /dev/null
--direc
tory /etc --one-file-system --listed-incremental
/var/amanda/gnutar-lists/pac_et
c_1.new --sparse --ignore-failed-read --totals .
Total bytes written: 30720 (30kB, 462kB/s)
.....
---
(and so on for other disks on the same host.)

Alex

-- 
Alexander Jolk         /         BUF Compagnie
tel +33-1 42 68 18 28 /  fax +33-1 42 68 18 29