I need to allow Everyone on the internet to attach a document

I have a form that I allow everyone on the internet to fill out.  The user needs to be able to add multiple documents, so I have created another table "Add Supporting Documents" to allow them to upload multiple documents to one form.  

When the everyone on the internet user tries to attach it takes them to log in.  
I have made sure to give them access to the form table and the add supporting documents table.  

"Add Supporting Documents" button Code:  

URLRoot() & "db/" & [_DBID_CAR_SUPPORT_DOCUMENTS] & "?a=API_GenAddRecordForm&_fid_7=" & URLEncode ([ID])& "&z=" & Rurl()