Question : Help creating a connector between Exchange 2003 and Exchange 2010

We are currently installing a new exchange server 2010 box to replace our exchange server 2003 (sbs) box.  

During the 2010 setup I told exchange to setup a connector between the 2 servers so that mail could flow back and forth.  This worked fine for the internal mail flow.

After the setup, I ran into an unrelated problem and had to delete the connector.

Question:  Without running setup again, how can I recreate the connector between Exchange 2010 and 2003?

Answer : Help creating a connector between Exchange 2003 and Exchange 2010

As described in the article: you need to follow the 889713 article to determine the channel of your W2k3 installation and compare it with the channel for which you obtained the key; they probably don't match ("The product keys that are used during installation are unique for each channel and cannot be interchanged with another channel.").
The channel, the SKU, the language, and the key *have* to match, otherwise you won't be able to upgrade.
If you can't obtain a key matching the channel AND the SKU of the W2k3 base install, you need to check if options 2 or 3 under "Upgrade options" will help (which obviously requires access to a CD1 of a channel and SKU matching your R2 key); "However, you must use option 2 or option 3 if the channel, the SKU, or the product key does not match the existing Windows Server 2003 installation."