Problem with Aastra 55i Phone

I have 12 identically configured Aastra 55i phones connecting to an Asterisk 1.4.0 server. The phones are behind Linksys routers, and the server is across the WAN and not nat’ed. Here is a crude drawing of the network.

55i----linksys----internet----asterisk

One of the phones is giving me the following errors on a very frequent basis. I have upgraded the firmware in the phone to the lastest, and I have set the phone back to the factory default and reapplied my configuration. I’m going to include the phone’s config files below the error. Also, I’m using Thirdlane PBX Mgr as the front end because I need multi-tenant capability, but I doubt that has anything to do with this. Can anyone help me understand what might be happening here?

Thanks!

[Aug 16 08:15:10] NOTICE[2833]: chan_sip.c:12001 handle_response_peerpoke: Peer ‘100-env’ is now Reachable. (107ms / 9000ms)
[Aug 16 08:16:10] WARNING[2833]: chan_sip.c:6400 determine_firstline_parts: Bad request protocol OK
[Aug 16 08:16:10] NOTICE[2833]: chan_sip.c:14563 handle_request: Unknown SIP command ‘SI10000P/2.0’ from ‘xxx.xxx.xxx.xxx
[Aug 16 08:16:11] WARNING[2833]: chan_sip.c:6400 determine_firstline_parts: Bad request protocol OK
[Aug 16 08:16:11] NOTICE[2833]: chan_sip.c:14563 handle_request: Unknown SIP command ‘SI10000P/2.0’ from ‘xxx.xxx.xxx.xxx
[Aug 16 08:16:12] WARNING[2833]: chan_sip.c:6400 determine_firstline_parts: Bad request protocol OK
[Aug 16 08:16:12] NOTICE[2833]: chan_sip.c:14563 handle_request: Unknown SIP command ‘SI10000P/2.0’ from ‘xxx.xxx.xxx.xxx
[Aug 16 08:16:13] WARNING[2833]: chan_sip.c:6400 determine_firstline_parts: Bad request protocol OK
[Aug 16 08:16:13] NOTICE[2833]: chan_sip.c:14563 handle_request: Unknown SIP command ‘SI10000P/2.0’ from ‘xxx.xxx.xxx.xxx
[Aug 16 08:16:14] NOTICE[2833]: chan_sip.c:14934 sip_poke_noanswer: Peer ‘100-env’ is now UNREACHABLE! Last qualify: 107

aastra.cfg

aastra registration

backlight mode: 2
sip proxy ip: xxx.xxx.xxx.xxx
sip proxy port: 5060
sip registrar ip: xxx.xxx.xxx.xxx
sip registrar port: 5060
sip registration period: 120
sip registration retry timer: 20
sip registration timeout retry: 30
sip registration renewal timer: 30
sip rtp port: 10000
sip use basic codecs: 1
auto resync mode: 3
auto resync time: 00:00

time server1: xxx.xxx.xxx.xxx
time server2: xxx.xxx.xxx.xxx
time server disabled: 0
time zone name: US-Eastern
time zone code: EST
dst config: 2

download protocol: FTP
ftp server: xxx.xxx.xxx.xxx
ftp username: xxxxxxxxxxxxxxx
ftp password: xxxxxxxxxxxxxxx

sip dial plan terminator: 0
sip digit timeout: 5

sip blf subscription period: 120

directed call pickup: 1
sip intercom type: 2
sip intercom prefix code: *98
sip intercom line: 1
sip intercom mute mic: 1
sip allow auto answer: 1

prgkey1 type: directory
prgkey2 type: callers
prgkey3 type: speeddial
prgkey3 value: *85
prgkey4 type: dnd
prgkey5 type: speeddial
prgkey5 label: FWD On
prgkey5 value: *72
prgkey6 type: speeddial
prgkey6 label: FWD Off
prgkey6 value: *73

.cfg file

aastra line configuration

sip line1 auth name: 100-env
sip line1 password: xxxxxxx
sip line1 user name: 100-env
sip line1 display name: 100-env
sip line1 screen name: Keith - 100

aastra phone options

softkey1 type: speeddial
softkey1 label: "Ext Pickup"
softkey1 value: **
softkey1 states: idle

softkey2 type: speeddial
softkey2 label: CallReturn
softkey2 value: *69
softkey2 states: idle

softkey3 type: speeddial
softkey3 label: Voice Mail
softkey3 value: *85
softkey3 states: idle

softkey4 type: dnd
softkey4 label:
softkey4 value:
softkey4 states: idle connected
softkey4 menugroup:

softkey5 type: speeddial
softkey5 label: FWD-On
softkey5 value: *72
softkey5 states: idle
softkey5 menugroup:

softkey6 type: blf
softkey6 label: Keith (105)
softkey6 value: 105