This error seems to crop up when Adobe PDF has either been installed, or in my case recently, when a user profile migration doesn't go quite as expected, but that's another story entirely.
How to really fix the Excel "Compile Error in Hidden Module" error:
Error message as follows when starting up or shutting down Excel:
"Compile error in hidden module: DistMon"
Looks like this:

Find the following file: "PDFmaker.xla"
Delete the file and the problem should stop.
How to find the file:
It will be in either "Office\XLStart" or "Excel\XLStart"
Go to Start | My Computer| Drive C: | Docs and Settings | User Name | Apps Data | Microsoft |
Or just do a search for the "PDFmaker.xla" file
If you can not see the file, make sure you can view "hidden files".
To view hidden files open My Computer | Click on "Tools" in tool bar | "Folder Options" | "View" tab | now click on the radio button next to "Show hidden files and folders" if it is not already checked off.
You may also want to uncheck the box next to "Hide extensions for known file types"
How to really fix the Excel "Compile Error in Hidden Module" error:
Error message as follows when starting up or shutting down Excel:
"Compile error in hidden module: DistMon"
Looks like this:

Find the following file: "PDFmaker.xla"
Delete the file and the problem should stop.
How to find the file:
It will be in either "Office\XLStart" or "Excel\XLStart"
Go to Start | My Computer| Drive C: | Docs and Settings | User Name | Apps Data | Microsoft |
Or just do a search for the "PDFmaker.xla" file
If you can not see the file, make sure you can view "hidden files".
To view hidden files open My Computer | Click on "Tools" in tool bar | "Folder Options" | "View" tab | now click on the radio button next to "Show hidden files and folders" if it is not already checked off.
You may also want to uncheck the box next to "Hide extensions for known file types"