cron.daily scripts won't run

I just found the solution for my problem that some of the scripts in /etc/cron.daily would never run, and I thought i'd share it..

This might be really obvious for some of you, but I thought if I blog this with a clear title it might be of help for some other people as well. I had problems googling this myself, so here is my solution:

Apparently those scripts are not allowed to have extensions such as .sh or .php.. when this is the case the scripts will simply be ignored..