I had this problem too. I found the answer somewhere in this forum, I think. Anyway, the answer was that the Trend Micro program does not contain a Trojan, but does contain unencrypted malware defintions which avast! will see as a Trojan. The answer is to turn off on-access protection (right click the avast! globe) before launching the Trend program- not forgetting to turn it back on when the Trend scan has finished, of course.
Do a search to find the detailed answer in this forum which I just summarised above.
I have sent the Trend program to avast! but I probably wasn't the first. The avast! team know about the occurrence, and have explained the reason and given an answer on this forum, so they might be mildly annoyed if we keep sending them the thing in emails.