download pdf : file not found

hello everyone
I have a strange behavior and can’t get it working :
? I am in development with linux machine Latest scriptace level 8.1
? I generate a pdf of a form
? I can “print” (view) the result
? I can locate the pdf and log files in the temp directory
? The tmp directory has 777 permissions

But, when i Click on download; I get an error message : “file not found”

What did I do wrong?

Regards
Gilles Bonnet

Forgot to tell that this only happens on forms. Export in pdf works fine on grid applications