Renaming files/File not Found

[Jerry62712]

I'm getting this error:
File not found: file:/C:/Flex%20Builder%203/FSCalc2/bin-debug/FSCalc2.html

I tried using FlexBuilder->File->Rename to change the names of several files. I changed:
src -> classes
src -> css
to
src -> DHSClass
src -> DHScss
and back after getting errors.

Now I can't run the application with the above error.
1) is that the correct way to rename files?
2) if not, how?
3) what file is missing the "FSCalc2.html?"
4) how do I fix this?

[Jerry62712]

I created the entire application over again and still get:
File not found: file:/C:/Flex%20Builder%203/FSCalc/FSCalc/bin-debug/FSCalc.html

when I try to run the application. In the Flex Builder, I see:
Severity and Description Path Resource Location
unable to open 'C:\Flex Builder 3\FSCalc\FSCalc\classes' FSCalc Unknown