I've had the same problem, and this is how I resolved it:
Open your ANT directory and check that all the ANT files exist (like directories for bin,lib,etc...)
I found my ANT directory was abnormal, just bin was there, the others like lib were missing. (I'm not sure what caused this)
If you have missing files/directories, unzip the apache-ant-1.9.4-bin.zip again, and make sure all the files exist.
