That was true for AutoCAD 2012 as well, which is why we started hitting this problem then.
To update my own comments, I have noticed a couple of strange things in AutoCAD, but because I essentially forgot all about this Fiberworld stuff, I never tested things with Fiberworld = 1, so I'll have to go back and do that to see if the strange things were related to fiberworld or not.
for 2012, you didn't have to use .NET 4.0, so you could use VS 2008 and avoid these problems, as i understand it, this won't be possible for 2013
excerpt from DevNote:
AutoCAD 2012 targets .NET Framework 4.0. This means you have to use VS2010 to debug your .NET application....
Concerning compiling and running a .Net or mix-managed application for AutoCAD 2012, you can still use VS2008 SP1, but as it doesn't support .Net Framework 4.0, you won't be able to run your application under the debugger.
As far as I'm concerned that says that you have to use VS 2010 in order to debug a .NET addin for AutoCAD 2012. This is not the only article that originally gave me that indication (a year ago), but it is the only one I was able to find today.
I am using AutoCAD 2012, VS 2008 and happily debugging
I just had to edit acad.exe.config, if this will be possible with 2013, then everything is OK for me.
But the note that ".NET Framework 4 needs to be targeted in Visual Studio." indicates, that it's a change compared to 2012, because it was an article about news in 2013.
I am having major issues with this FIBERWORLD problem. I am running VS2010 with AutoCAD 2013 on a WIndows 7 64 bit machine targeting 64 bit user machines. These are several large drawing generator programs written in VB.NET, mostly native .NET with a little COM Interop here and there. (These programs worked fine in R2009.)
If I leave NEXTFIBERWORLD set at 1, then I get the error while debugging in VS at random points where it loses the source code.
If I set NEXTFIBERWORLD to 0 then the programs start to do crazy things like not activating a drawing that has just been opened or added, which causes the rest ofthe program to fail.
So, if I want the programs to run correctly in order to debug them, I can't debug them. Catch 22.
Still waiting on some ideas for how to proceed from Dev Help.
Image of the error message for the “No Source Available” while debugging attached.