Cannot see the "Trust this Add in" button for Anna VAT spreadsheet

Hello,

I wonder if you could help me with this. I cannot see the "Trust this Add in" button for Anna VAT spreadsheet that allows uploading to HMRC of VAT returns. The Anna VAT Add In is not listed as an Excel add In and therefore I cannot get access to the functionality to upload a VAT return. I am using Excel 2010. The Add In is not listed on the Add Ins tab in Excel nor is it shown if I choose File / Options / Add-ins. I have tried closing Excel and reopening it and downloading the file from the Anna website again but not been able to fix it. I would be grateful for any suggestions. Many thanks.