AppleScriptTask will not run

I am trying to get an Excel spreadsheet developed in Windows to work on a Mac. I have included two AppleScriptTasks that check that files exist and send emails. On the Mac on which I'm working, these perform successfully. However on a colleague's Mac, he gets a Run-time error '5 Invalid procedure call or argument' each time. Everything looks similar on both. The only difference I can see is that on my Mac, in System Preferences | Security & Privacy | Automation, the box on the right contains 'Microsoft Excel' and 'System Events' (ticked). Would this be the reason that the AppleScriptTasks won't work? If so, I can't see how to add Excel on his Automation tab. Any thoughts would be appreciated.

Or does anybody else use AppleScriptTask in Excel? If so, do you have Excel listed in System Preferences | Security & Privacy | Automation ? Then I can at least see if this may be the cause of my problem or whether I need to look elsewhere. Thanks.