TMG Security Credentials Popup

[ICTHUS]

We have been using TMG for a number of years now.

 

It works fine and category filtering is great.

Recently though the popup for Windows Security has started popping up on certain websites like AMAZON for instance.

 

A use can type their network logon and password and tick “remember my credentials” box, but it keep popping up. I cannot see what the solution is. It is baffling. The TMG logs don’t give any clue either. Happens for all users going through TMG, even us administrators.

 

Anyone care to hazard a guess on what this is please?