We are running Directory Opus 8.2.2.5 and have experienced this problem with earlier versions as well.
If we are viewing a folder with Microsoft Excel 2003 (sp2) files and the viewer pane is on we can see the output in the viewing pane, when we try to open the spreadsheet in excel from the opus 8 window, Excel fails to open (although it appears to be in the taskbar we can not open it).
When I go to the task manager Microsoft Excel appears as running and there are no processes running higher than normal. To shut out of excel we have to end the task.
Has anyone else experienced this? We have removed and reinstalled Opus 8 to no effect.
I don't believe you should be editing a file in Excel (or any other application) that you are viewing in the Opus Viewer Window or Opus Viewer pane (or any other viewer) at the same time.
You are just asking for trouble. That would be like me trying to drive my car, while my mechanic is working on the engine at the same time, which is probably not a good idea.
Try turning on Preferences / Plugins / ActiveX Document: Create temporary copies of Office files.
That may allow you to view a file in the viewer while also loading it into a separate Excel window, since it copies the files to your temp directory with a new name before opening them. Of course, it will break macros etc. which depend on file names or other files in the same directory, but those are uncommon.
The problem you're seeing isn't specific to Opus. All Opus really does to view an Excel file (via the ActiveX route -- the MultiView plugin is different) is launch Excel itself within the viewer pane.
You'll see the same thing happen if you try to open two instances of Excel and load the same file into both. It's all part of the wonderful design of Microsoft Office.
Other ways around the problem:
Close the viewer before opening the file. (Of course.)
Configure the ActiveX plugin so that it doesn't handle XLS, DOC, etc. files and instead use the MultiView plugin. This requires that you install some DLLs which you can get for free with a number of other products, but once installed the Opus viewer can display Office documents without using Office itself which means the real Office applications don't trip over themselves.