Prestahop won't accept write permissions in step 2

[T-bird]

I've just upgraded to 1.5.4.1, or at least I'm trying to. I can't get past step 2 as it says I need to change the recursive write permissions for files and folders in modules, however I've tried chmod 755, 775 and 777 and it just isn't having it. In desperation I've changed every single folder on the site to 777 and it still says I need to change them in modules! Any idea what's going on here?

 

It also says I need the Mcrypt extension, however this isn't an option on my server. Is there a way to disable the requirement for Mcrypt?

 

Thanks.