Using the last Eclipse (Galileo).
I am trying to set a break point at some point of a the main method.
But Eclipse will not let me do it, instead it says at the bottom of the screen in red lettering "a break point already exists at the next valid location --- line 140".
Line 140 is the end of the main method.
So it does set a break point there, but why not where I wanted?
Other files in the project do not exhibit that problem.
Open your project.
Switch to Debug perspective (Window->Open Perspective->Debug)
Select the Breakpoints tab. Here you will see a list of all the set breakpoints. Does your main method line 140 show up here?
Click on Remove All Breakpoints in the Breakpoints tab.
Switch to Java perspective and retry setting the breakpoint