Error Message Opening Engage Interaction

We are using the Articulate Suite '09 and have several Engage interactions embedded in training presentation.  Just in the last few days, we began having issues with some of the interactions, like audio disappearing from the interaction tabs.  After attempting to correct this situation another, more serious error occurred today.  On trying to open the interaction from within the PowerPoint slide, the error "this project cannot be opened.  Please make sure it is not already open in another instance of the application and try again."  After clicking the OK button, a second message displayed "Unable to open Interaction HEVR.intr for editing.  If this interaction is already open in Articulate Engage then please close it and then retry."  The answer to that question is no the interaction was not open in Engage.  In fact, the developer rebooted his computer and tried a second time, with the same results.

What options are available?  Will we need to delete the interaction and create a new one?  Help is, as always, greatly appreciated.

Darrell