uploading files in phpWiki

Hello,

I am trying to upload files in a new wiki installation that I've just put on 
my website. I am computer literate but not very tecchy, so you will have to 
bear with me...

I copied <?plugin Upload ?> on my wiki
homepage and the text field and the Browse and Upload buttons appeared
there, when clicking on browse and selecting a file and then click on
Upload, I get a message "Access denied: please log in to upload files"(see
image atttached wiki.gif) but I am signed in (see image attached wiki02.gif)
unless there is another way of logging in that I can't find...can you help?

I've used wikis before and I know you can do it but don't know how :(

Thank you!

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