Peter,
I don't have Encumbrance Management installed so I am giving you idea of how to use vba to stop popup of information window on some other GP window, just do the same with your Encumbrance Management window on which you want to disable this popup.
1. Open the window in which this message pops, go to tools menu>>Customize>>Add current window to visual basic.
2. Now again go to Tools>> Customize>> and now click Visual Basic Editor.
3.Editor will open, find your window and paste below code on the right hand side pan.
Private Sub Window_BeforeModalDialog(ByVal DlgType As DialogType, PromptString As String, Control1String As String, Control2String As String, Control3String As String, Answer As DialogCtrl)
If PromptString <> "" Then
Answer = dcButton1
End If
End Sub
Please note that instead of typing the prompt message , I am checking if not empty because our prompt string have different account and amount with different item, you can even make that string by reading the values from window but it would be hard for you.