Then you have a broken viewer. Get one that doesn't mind having the viewed file overwritten.
This happens to acrobat viewer. This is easy to confirm: open lyx, type a, view pdflatex, type b, view pdflatex, lyx says I cannot write on file 'newfile1.pdf'.
A workaround if you can't fix the viewer: Make a script/program that copies the temp file to a new unique name, and then launches your broken but preferred viewer.
This is close to the trick on the wiki (forget where), but it is certainly troublesome for this commonly used viewed.
Complaining to your viewer vendor might help too, but will likely be slow.
Exactly.
If we use a different temp file each time, how do we know when we can delete it?
Donot we remove all lyx tmp folder for each session? Bo
