Excel 2007 : File Open Attachment problem

Until a few days ago, if Excel were already running, and I clicked on an attached file (in an email) the file would simply open within the Excel program I was running.

Now if Excel is already running, clicking on an attachment tries tries to start the Excel program again, resulting in conflicts with PERSONAL file, and so forth.

Now, If Excel is not running, clicking on an attachment will start Excel, but not necessarily open the file I clicked on, whereas it used to, a few days ago.

This phenomenon does not occur with other types of attachments. PDF files, DOCX files, all work fine. This leads me to believe that there is some setting in Excel causing the problem. Otherwise I might think the fault was in an Outlook setting.

Any suggestions? My productivity is suffering. My work-around is to save each file attached to an email, go to the Excel program and File Open.

I have learned the answer:

There was a check - box selected that shouldn't be:

Office Button
Excel Options
Advanced
General
Ignore other applications that use Dynamic Data Exchange (DDE)
Clear checkbox

I am not aware of how it became 'checked', but it was