Assign Predecessors window - no show

Hello,

This might be something new as I could not find it in the "support" website. I thought to check with the community before requesting support.

I am using Primavera P6 Professional R15.2.

When adding relationships using the Details in the Activities workspace/view, the Assign button when clicked did not show the Assign Predecessors window !! It did not work in the Activity Network view, as well. The focus seemed to move from P6 to somewhere else.

However, the Assign Successors window works fine when the Assign button is clicked; and, the focus goes to the Assign Successors window.

Any help would be appreciated.