use of "on error" to find intersection

Hi I want to use the "on error" function to assign a value after an error occurd, however it seems that the "on error" function is not able to cope with an undefined variable, see example.

In this case it is obvious that there is no sollution, however I would like to continou with the value 0 (or whatever) if no solution can be found. Can somebody help me how I can tackle this problem?

I have also attached the example.