How did you set things up? Did you drop those two jars into
ant's lib directory along with the required and optional jars (especially ant-commons-net.jar)?
It sounds like it cannot find ant-commons-net.jar.
My ant/lib directory has commons-net-1.4.0.jar and jakarta-oro-2.0.8.jar in it and my ftp tasks work. I removed ant-commons-net.jar from ant's lib directory and ran the build with an ftp task in it and got a rather long error message that sounds like what you said you got.
There are other ways to set this up besides dropping the jars in ant's lib directory, but you need to follow the instructions carefully due to the classloader issues.
[ May 17, 2005: Message edited by: Carol Enderlin ]