I don't think that's your issue but dialog boxes are not supported on InfoPath forms when they run on a browser, they can only show up when you fill your form using InfoPath Filler.

There is only some client side code that on the main drop down change calls the data view's "_dopostback" function, anyways I've changed my solution so that now my secondary drop down is populated via SPservices whenever the main drop down select value is changed, with a the SPservices caml query containing it's value, it works fine, thank's again for replying!

Thanks for your'e reply, the thing is i'm using the main drop down as a control parameter in my data view's select command, and once I select it's value instead of causing post-back i'm calling the data view's manual refresh function which causes only partial post back - __doPostBack('ctl00$m$g_41f15437_f263_46cb_9aa1_22c7c42f7f59‌​$ctl01','__cancel'); now i need to add another filter using this secondary cascading dropdown, and i want it to populate without postback for the entire page, if that's possible.