Ajax url error

Ajax url error

Following is a snippet of ajax code which works fine if the call is made from home page.
If I use it in another page I get 404 error code regarding the "url:" option.
As seen from the code the url is "wp-content/plugins/myplugin/build_responsive_css.php"
In case of another page say "page1" I get the following error in the Chrome consol:
page1/wp-content/plugins/aaa-responsive-design-helper/build_responsive_css.php 404 (Not Found)
How can I solve that?
Regards
I. Sher