Opening an XLS file created by CA Output Management Web Viewer (export report) with Microsoft Excel (starting at the 2007 release) will issue the following message to the end user:
The file you are trying to open, '[filename]', is in a different format than specified by the file extension. Verify that the file is not corrupted and is from a trusted source before opening the file. Do you want to open the file now?
(Yes | No | Help)
This is something that cannot be addressed any differently from CA Output Management Web Viewer. In order to support Excel spreadsheets WITHOUT requiring that Excel be installed on the server, CA Output Management Web Viewer creates the XLS file using a specially formatted HTML file with an XLS extension. Starting with Excel 2007, Microsoft implemented something they call "Extension Hardening," which (to make a long story short) causes the "different format than specified by the file extension" message to be produced.
If you search the web for "Extension Hardening" and "XLS" you should find a lot of information on the topic, but the bottom line is if you are using Excel 2007 and you want to see the report you exported from the CA Output Management Web Viewer, you should click the "Yes" button in the message. It's an extra step, but with Excel 2007, there is no easy way around it.
There is a method for the end user to suppress the message (a registry change to the end-user's computer) and we have verified that the technique works, but it is not something that CA recommends.