Try downloading 3.7.3 in Safe Mode with Networking.
I use Norton Security and when downloading the free version on another Win 7 laptop, Norton gave it a clean bill of health.
As for the compatibility problem, while it downloads it to Program Files (x86) I don't know if it's architecture specific and the program downloads the correct version for the system - but I had no problem downloading and running on a 64 bit system.
Having Googled false positives by Sonic Gateway, there seem to be quite a few links of complaint.