I saw the same issue in many different locations and even after a good portion of googling, I could not resolve it. What I am trying to do (the bigger picture) is to go through
If you are using Eclipse IDE and facing this issue, here is something that worked for me. Go to : Window > Preferences. Find the Ant option on the left side.
Expand it and you will find ANT Runtime. Select that option and check the jars included in the Classpath tab.
Select the Add External Jar's option. Now go to the ant home folder in your system. Go to the lib folder and add all the jars / missing jar files.
this will resolve the missing dependency for ant-build.
Hope That Helps!