Only Rev.7170 supports E2K7; from the Backup Exec UI, do Help > About and identify the revision ... either 11.0.6235 or .7170. If you do not have 11.0.7170, the download link is here:
http://esdownload.symantec.com/akdlm/CD/MTV/BEWS_11D.7170_32BIT_VERSION.zip
The agent is identical, regardless of the version of Exchange you are backing up so, since you already have Exchange agents, you're in good shape that way.
If you DO have Rev.7170, I would need to see the actual text of the error.