My guess is that there is a permissions deficiency in his account that is not obvious. It is possible for a lack of %Admin_Operate:U can deny access to certain pages in the Management Portal; see the following documentation https://docs.intersystems.com/iris20252/csp/docbook/DocBook.UI.Page.cls?...

"It controls access to various pages in the Management Portal, including the System Operation page."

Are you certain that there are no permissions differences between his account and others'? You mentioned using a test account with the same permissions - was this test account cloned from your colleague's?

Another possibility is that he is attempting to access a different page in the management portal than you are. Not all pages in the Management Portal are created equal - I would try sending him a "clean" link to the Management Portal landing page to make sure he isn't trying to access a page he doesn't have permissions on.

If neither of these avenues of investigation bear fruit (and no one else here comes up with another answer), I would contact Support - they have the most experience dealing with permissions minutiae. 

I hope this helps and that you can get this resolved soon - permissions issues can be very frustrating, speaking from personal experience.

What version of IRIS/Cache was this class imported from? In 2024.1, the %Collection.ListOfObj class doesn't have a parameter called 'Collection': https://docs.intersystems.com/iris20241/csp/documatic/%25CSP.Documatic.c... 

I am fairly sure you can just remove it without issue.