Here's all the rest of the information I could find:
This error can occur if the directory version of the proxy address generator (the File-Version object attribute) does not match the corresponding actual dynamic link library (.dll) file versionof the e-mail address generator.
To join the site, follow these steps on the existing server in the site. To upgrade Exchange Server by either applying a service pack or by upgrading to a newer version of Exchange Server, follow these steps on the server that you are upgrading:
1. Check the version of the proxy address generator .dll files that are located in the following locations:
- For Intel servers:
C:\Exchsrvr\Addresses\Ccmail\I386\Ccmproxy.dll
C:\Exchsrvr\Addresses\Ms\I386\Pcproxy.dll
C:\Exchsrvr\Addresses\SMTP\I386\Inproxy.dll
C:\Exchsrvr\Addresses\X400\I386\X400prox.dll
- For Alpha servers:
C:\Exchsrvr\Ccmail\Alpha\Ccmproxy.dll
C:\Exchsrvr\Ms\Alpha\Pcproxy.dll
C:\Exchsrvr\SMTP\Alpha\Inproxy.dll
C:\Exchsrvr\X400\Alpha\X400prox.dll
2. Compare the version number with the version found in the Exchange
Server Administrator program under Site\Configuration\Addressing
container. Select the E-Mail address generators object on the left hand
side. The right hand side will display the various Email address
generator installed on this system such as Internet E-mail address
generator for I386. Select the Email address generator that is listed
in the error message. When you click to select the properties of that
object, the Version information of that Dynamic Link Library will be
displayed.