Mirroring Connection Problem

Greetings,
I am trying to setup database mirroring on two seperate servers running SQL 2005 SP2. I would eventually like to add a witness. I have tried the SQL wizard with and without a witness to no avail. I am now trying to use certificates. I have changed both servers to use a domain administrator logon to run the services. I am getting the following message each time I try to alter the database on the principal after I have setup everything on the mirror server.
Msg 1418, Level 16, State 1, Line 1
The server network address "TCP://10.99.99.02:5022" can not be reached or does not exist. Check the network address name and that the ports for the local and remote endpoints are operational.

Here is the TSQL statements I am using on the principal server:
-- Step 1
create master key encryption by password = 'xxxxxx'

-- Step2
create certificate Principal_Cert
with subject = 'Principal Certificate',
expiry_date = '12/31/9999'

--Step 3
backup certificate Principal_Cert to file = 'c:Principal_cert.cer'

--Step4
create endpoint Endpoint_Mirroring
state = started
as TCP (listener_port = 5022, listener_ip = all)
for database_mirroring (authentication = certificate Principal_Cert,
encryption = required algorithm AES,
role = all)

-- Backup database SPOT - go to Mirror Server

-- Step 5 after setup on Mirror server

create login Mirror_login with password = 'xxxxxxxx'

-- Step 6
create user Mirror_user for login Mirror_login

--Step 7
create certificate Mirror_Cert
authorization Mirror_user
from file = 'c:Mirror_cert.cer'

--Step 8
use master
grant connect on endpoint::Endpoint_Mirroring to [Mirror_login]

-- Step 9
alter database spot
set partner = 'TCP://10.99.99.02:5022'

**** Getting message here **********

-- Checks

select * from sys.server_principals

select * from sys.sysusers

select * from sys.certificates

select * from sys.database_mirroring_endpoints

SELECT e.name, e.protocol_desc, e.type_desc, e.role_desc, e.state_desc,
t.port, e.is_encryption_enabled, e.encryption_algorithm_desc,
e.connection_auth_desc
FROM sys.database_mirroring_endpoints e JOIN sys.tcp_endpoints t
ON e.endpoint_id = t.endpoint_id

Here is the TSQL statements I am using on the mirror server. This all works fine.

-- Step 1
create master key encryption by password = 'xxxxxxxx'

-- Step2
create certificate Mirror_Cert
authorization dbo
with subject = 'Principal Certificate',
EXPIRY_DATE = '12/31/9999'
ACTIVE FOR BEGIN_DIALOG = ON

--Step 3
backup certificate Mirror_Cert to file = 'c:Mirror_cert.cer'

--Step4
create endpoint Endpoint_Mirroring
state = started
as TCP (listener_port = 5022, listener_ip = all)
for database_mirroring (authentication = certificate Mirror_Cert,
encryption = required algorithm AES,
role = all)

-- Step 5

create login Principal_login with password = 'xxxxxxxx'

-- Step 6
create user Principal_user for login Principal_login

--Step 7
create certificate Principal_Cert
authorization Principal_user
from file = 'c:Principal_cert.cer'
ACTIVE FOR BEGIN_DIALOG = ON

--Step 8
use master
grant connect on endpoint::Endpoint_Mirroring to [Principal_login]

-- Restore Step

RESTORE DATABASE SPOT
FROM DISK = 'C:SPOT.bak'
WITH NORECOVERY

RESTORE log SPOT
FROM DISK = 'C:SPOT_log.bak'
WITH NORECOVERY

-- Step 9
alter database spot
set partner = 'TCP://10.99.99.01:5022'

-- Checks

select * from sys.server_principals

select * from sys.sysusers

select * from sys.certificates

select * from sys.database_mirroring_endpoints

SELECT e.name, e.protocol_desc, e.type_desc, e.role_desc, e.state_desc,
t.port, e.is_encryption_enabled, e.encryption_algorithm_desc,
e.connection_auth_desc
FROM sys.database_mirroring_endpoints e JOIN sys.tcp_endpoints t
ON e.endpoint_id = t.endpoint_id

select *
FROM sys.database_mirroring_endpoints


Does anyone have any ideas?

Thanks