invisible join

Hi Gurus,

I was trying invisible join explained in http://odiexperts.com/invisible-join/.
But somehow this trick is not working for my interface.
I have created 1 variable VAR_1 and 3 tables EMP1,EMP2 and EMP3 with identical columns EMPNO and AGE.
and used EMP1,EMP2 as source & EMP3 as target.
with join condition EMP1.#VAR_2=EMP2.#VAR_2

while clicking on tick icon on property inspector pan for join, I am getting error "ODI-15631: Connection information not available"

What could be the reason behind this issue.