why am i getting a security certificate has expired or is not yet valid error when opening outlook 07 in an exchange 07 network?

The exchange 2007 certificate is meant to be temporary until you can purchase one from an Internet Cert Provider as per
http://msexchangeteam.com/archive/2007/04/30/438249.aspx

However, you can recreate a new self signed cert by following this article.
http://technet.microsoft.com/en-us/library/aa998327(EXCHG.80).aspx

is there a way for me just extend the existing certificate that has been running for a year?

where are these certificates at?

Check the second link.  The first example is a cmdlet to create a new self signed cert.  Which is what you want to do.  

I have had the same problem and found that updating my IIS certificate on the Exchange 2007 server solved the problem.

Hello this might help if you have a self signed certificate which I believe Exchange 2007 creates on the first install. You just have to renew your certificate. You can get your current certificate thumbprint from the certificates MMC console.
Command to get certificate services and info. Thumbprint should be in  .
 U:\>Get-ExchangeCertificate -Thumbprint "e1 44 7c 52 69 f3 f4 72 7e a9 26 e
d e6 7f 10 e4 a4 e5 2f ed"
Output:
Thumbprint                                                  Services       Subject
----------                                                  --------             -------E1447C5269F3F4727EA926EDE67F10E4A4E52FED  SIPUW      CN=polarbear
You should note which services are enabled on the current certificate. I believe S=SMTP,I=IMAP,P=POP,U=Unified Messaging, W=IIS dont quote me on the exact service but those should be pretty close.
Command to clone and renew certificate
U:\>Get-ExchangeCertificate "e1 44 7c 52 69 f3 f4 72 7e a9 26 ed e6 7f 10 e
4 a4 e5 2f ed" | New-ExchangeCertificate
Output:
Thumbprint                                          Services   Subject
----------                                                  --------   -------
20C15A1BDAD79FC57848EE78AE7A88368912D468  .....      CN=polarbear

Notice there seems to be no services assigned to the above cert Ouput.
Rerun command to get certificate services and info.
 U:\>Get-ExchangeCertificate -Thumbprint "20 c1 5a 1b da d7 9f c5 78 48 ee 7
8 ae 7a 88 36 89 12 d4 68"


Output:
Thumbprint                                                  Services   Subject
----------                                                  --------   -------
20C15A1BDAD79FC57848EE78AE7A88368912D468  SIPU.      CN=polarbear

As you can see all default services were loaded with the exception of IIS.
Now enable the certificate with the below command you can specify which services to include in the certificate in this case I have all the certificates enabled on the new certificate.
U:\>Enable-ExchangeCertificate -Thumbprint "20 c1 5a 1b da d7 9f c5 78 48 e
e 78 ae 7a 88 36 89 12 d4 68" -Services "IMAP, POP, UM, IIS, SMTP"

Run the command again to get certificate services and info and verify its correct.
 U:\>Get-ExchangeCertificate -Thumbprint "20 c1 5a 1b da d7 9f c5 78 48 ee 7
8 ae 7a 88 36 89 12 d4 68"

Thumbprint                                                  Services   Subject
----------                                                  --------   -------
20C15A1BDAD79FC57848EE78AE7A88368912D468  SIPUW      CN=polarbear

OK, so my certificate issue is fixed but that opened a whole new can of worms with Outlook 2007 and free/busy data!!!  After days and days of looking for info I am no closer to a solution.
And the articles on the web....some of them are good other are really bad!!!

I have tried just about every single one out there and checked and double check but I am still stuffed!!!!

I can see why some guys are really upset with MS!!!!!!!!!!!!!!

Hey Vnoome,

I'm not sure what your particular setup is like but my originally posting was geared towards mark319 and to those who had an expired self signed certificate from Exchange 2007. I found another expert exchange link that might help:
 http://www.experts- exchange.com/Software/Server_Software/Email_Servers/Exchange/Q_22840374.html  
You might be better off opening a new problem for this other issue with your specific environment details. I hope you have success.

http://exchangepedia.com/blog/2008/01/exchange-server-2007-renewing-self.html

Great link shows exactly how to renew your exchange 2007 cert in easy steps

mruxsaksriskul thanks for the info....
I managed to get my exchange problem resolved.....
Outlook/Exchange/OCS all happy now...

Certificates plays a huge part in the entire integration!!!

Just seeing fun and games ahead with Vista on Certificate Services on Windows 2003......