downloads suddenly not working, puzzelled

Problem; downloadable feature is not working. When the download button is pressed it tries to go to a page like 'main_page=download&order number etc."
but it just hangs as if it cannot find the page.

The pertinent details; 1. I know how to setup downloadable products and they were working not too long ago.
2. the problem is not the order status, download time or number expiry, all that is set correctly and the files
are in the download folder and showing with green lights in the downloads controller. The download is enabled
in my account with remaining downloads available and the download button is there.

So, 'any ideas as to what else might cause a problem with downloads ?

At this point I am stumped. Either I inadvertently changed something very periferal
and didn't realise it or the webhost has changed something.

If I knew where to start looking it would help.

Many Thanks,
Sheryl

I tried the php debugging tool and it shows this;

PHP Warning: mkdir() [<a href='function.mkdir'>function.mkdir</a>]: Permission denied in /home/credence/public_html/zen/includes/modules/pages/download/header_php.php on line 132

I have no idea where line 132 is or if it means a permissions issue elsewhere or what.

I think I have solved this issue after reading about download delivery methods.

The pub folder must be set to 777 in permissions. (it was set to 755)

The odd thing is that I never changed the permissions of this folder and in fact
have never even looked at it. So something else changed on our hosting account
because the downloads were definitely working not too long ago, so either our
webhost somehow changed the permissions of that folder or something else
periferal to it has changed.

In any case setting to 777 seems to be the answer for me.