>Each page on this form is a container based class with lots of objects. Today I changed btcc_container btcc_ValStr method and added one optional parameter there. I also changed some calls to this method. Now I'm getting must specify an additional parameter error.

You should get that if you have code for that method in the subclass which lists fewer parameters than are listed in the parent class.

>I added set step on in btcc_ValStr method for btcc_container and it doesn't go to this point, it errors just before it. This method is defined only in this class, everythere down in hierarchy this method is empty.
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>How can I force my project to take my changes in consideration?

You usualy get this sort of confusion if you do a lot of editing, and debugging, and exiting the debugger via "Fix". Quit and reload is the only sure-fire thing to do. The "Class is in use " error message and "source out of date" are part of the same situation: in the first case, the object is still in memory (clear all helps). The rest comes from VFP's code caching, and the debugger always had some problems with seeing the older version instead of latest. Works OK most of the time, but when it doesn't, quit/reload. With VFP7's persistent command window, I don't really care.