So, to understand you correctly....are you saying that:
1. You had successfully used this same license with BESR 8.5 before upgrading to 2010?
2. You uninstall 2010, then installed 8.5 (into evaluation mode) and then tried to install the license?
If this is correct, try searching for vprosvc.rtc - if this exists, try renaming it and then restart the Backup Exec System Recovery service. Then try to add the license again.