Error: type doesn't support the "osfamily" attribute

Above error can come when executing an ant target. This happens because ant versions older than 1.7 do not support osfamily.

Solve it by,
1. If you're using a older ant version, replace 'osfamily' attribute in exec tasks with 'os' in your build file.
or
2. If you're using ant 1.7, see if an older version of jar is getting picked up. If you have a certain jar earlier in the classpath which has ant dependencies, it might load an older version. Move such jars to the bottom of the classpath.