deadlock during debug

Hi everybody,

I'm trying to find where inside my program appears the first NaN var.  So I created the following function:

logical FUNCTION testanan(var)

implicit none
real(8) var

if (var /= var) then
    print*, 'deu NAN na', var
    TESTANAN=.TRUE.
    READ(*,*)
endif

ENDFUNCTION
                 

I run in debug mode and when the message appears in the screen, I press pause to find out in which line the NaN appears. But when I do that, deadlock happens...

How can I identify where is my first NaN happens?

Regards