Invalid implementation version between Ant core and Ant optional tasks.

Hi!
I am new to DITA, and have installed all the components as dicussed on http://dita-ot.sourceforge.net/doc/installguide/installotoverview.html.

After completing the installation, when I run "ant all" to test the installation, I am getting the following error message:

Invalid implementation version between Ant core and Ant optional tasks.
 core    : 1.6.1
 optional: 1.6.5

 

Please help me to know where I am making the mistake during installation.

Thanks,
Vikas

 

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