100 Mb unicast, 10 Mb multicast??

[Clairvoyant1332]

I have several Sun SunFire V240 servers running Solaris 8 plugged into a 100 Mb switch. I was running a test of a multicast file transfer application that I wrote, which also has the option of doing the transfer in unicast mode. I found that, with one machine in particular, any multicast file transfers coming in or out of the box won't run any faster than 10 Mb. However, if I tell the app to run in unicast mode, the transfer runs at the full speed of 100 Mb.

Any idea what could cause something like this?

Thanks,
Dennis