Migration Assistant can't find connected Macs

I had to replace a crashed hard drive in my 2008 iMac (2.66 GHz Intel Core2 Duo) so I'm trying to use Migration Assistant to move my applications from a more recent Mac Book Pro (2.3 GHz Intel Core i7) to the new hard drive on my iMac. The iMac is running OSX 10.6.8 with Migration Assistant v3.0.4 and the Mac Book Pro is running 10.7.5 with Migration Assistant v4.1.2. When I set up Migration Assistant in both computers they aren't able to connect. I don't get the screen that asks me to input the 6-digit code number. The two computers are connected via Ethernet and I can see the laptop on the iMac as a Shared Resource. So why can't Migration Assistant connect the two computers? About a year ago, when I bought the Mac Book Pro I was able to successfully use Migration Assistant to move files from the iMac to the new laptop without any problems at all. I've read through the other threads on the Support forums, and the only thing I can come up with is that there might be an issue of which user accounts I am using when trying to set up the migration. I have now tried various combinations using my wife's user account and mine, but with no luck.

Do I need to upgrade v3.0.4 Migration Assistant in Snow Leopard? I did an OS download just yesterday to maek sure each machine was using current versions of the software. The current version of Snow Leopard came with MA 3.0.4. Will MA 4.1.2 work with Snow Leopard? And is that even relevant to my problem? I have the Mountain Lion OSX Installer but have not installed it yet since our color laser printer will not support Mountain Lion.

I'm hoping I can figure this out without having to make another trip to the local Genius Bar (an hour's drive from my home). Does anyone have any ideas why Migration Assistant can't connect these two computers?

Thanks.