Cannot Drag/Drop Text in VB.Net Windows Forms - Worked Previously

I have a windows form VB.net (2005) application that uses drag drop is several places for dragging text from documents (MS Word, Web Page, etc) and dropping the text into a textbox or a richtextbox. For some reason this stopped working without any known changes to the program. Has been working fine for past 7 years. I have tried rebooting and turning the "Clicklock" mouse setting on/off, etc without any change in this. I am trying to develop additional drag drop but cannot test since it does function anymore. I am able to drag/drop text between MS Word documents w/o any issues. This is a Windows 7 OS.