Just upgraded a server from 2.6.0p2 to 2.6.1p1 and now amcheck outputs: 

Server check took 0.004 seconds
amcheck-clients: amanda/tcp unknown protocol

Amanda Backup Client Hosts Check
--------------------------------

(brought to you by Amanda 2.6.1p1)

The server is configured and compiled with 

./configure                                 \
--prefix=/opt/amanda                        \
--with-testing=av48-2                       \
--with-tmpdir=/var/tmp/amanda               \
--with-amperldir=/opt/amanda/perl           \
--with-config=top                           \
--with-user=amanda                          \
--with-group=disk                           \
--with-bsdtcp-security                      \
--with-amandahosts                          \
--with-tape-device=/dev/nst0                \
--with-changer-device=/dev/changer          \
--with-tape-server=wart                     \
--with-index-server=wart

I did a test by removing the `--with-testing' option 
and it works so has something changed in the config
step?

thanks,
jf