I'm using FlashBuilder 4 and errors are no longer highlighted in source view.
So there used to be a red symbol to the left of the source view page near the line numbers which you could mouse over to see the error.
This no longer occurs. I have restarted FB but no effect.
I searched the forums for this, but Adobe Forums no longer show links to search results (which makes the forums search capabilities useless).
I'm assuming your "Problems" view is displaying errors. Does double clicking on a problem affect the visibility of the problem marker in source view?
Can you post your Flash Builder log file (workspacedir/.metadata/.log)?
Mysteriously, now it is suddenly working.
Thanks for helping.