Word & pdf file in Lectora

Hi,wonder if someone could help me. I have a course that has some Word and pdf files embedded which should open when a button is clicked. I have done this a million times before, using the action On click- open/launch document and as the target I attach the Word document in question. This has always worked but now in this one particular course, when the button is clicked, the user gets thrown out of the Lectora course. And I have no idea why this is happening. Does anyone have any thoughts?Simone