"This breakpoint will currently not be hit. No symbols have been loaded for this document." What does this mean?

Question

I am debugging a C# Wpf program. It has been progressing normally. Breakpoints work etc.
I have just started VS 2019 up again to continue my work. I change a little bit of code and run a test. The breakpoint fails. I find when the program is running the breakpoint symbol is changed and there is the message shown in the title.
What can be the problem? One moment it works and then it does not. I have not changed anything other than a couple of lines of code.

I have tried "Clean" and "Rebuild Solution" to no avail.

Answer 1

Have you tried making these changes to your project properties, suggested in?:
https://stackoverflow.com/questions/2155930/how-do-i-remedy-the-breakpoint-will-not-currently-be-hit-no-symbols-have-been#answer-12262865