Each time I open Excel 2010 I get a message saying 'Normal.dotm: File format is not valid'. I simply click 'ok' and it goes away and all is fine. This does not appear when I open Word where all seems to be fine.
Any suggestions?
Thanks

Have you by chance copied the normal.dotm Word template into the following location: -

C:\Users\Your User Name\AppData\Roaming\Microsoft\Excel\XLSTART

If so then delete that normal.dotm file.

That suggests someone has configured your Excel application so that it tries to open 'Normal.dotm' - a Word template - instead of an Excel template.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

Just for the record 'Normal.xlsm' is not a template. See Change the default file format for saving workbooks . It is a macro-enable Excel workbook format.

Also I don't see how anyone could edit the MS 'Excel.exe' file to force it to use the Normal.dotm Word template. Excel uses the templates 'Book.xltx' and 'Sheet.xltx' stored in the XLSTART folder when it launches.

It would be interesting to see if @Windspeed finds a solution and what it was. Are you watching OP?

There is also another XLSTART folder in the Program Files\microsoft Office\Officenn folder, and you can configure a further startup folder in Excel options, so it may be worth checking those too.

@Debaser - You state "There is also another XLSTART folder in the Program Files\microsoft Office\Officenn folder" . There isn't a second XLSTART folder on my machine? I have looked in both 'Program Files' and 'Program Files (x86)' folders.

Just thought I would mention this in case other people look and don't find it. It may depend upon the version of Office that is installed?

It seems to have been moved, at least for 365, to Microsoft Office\root\Office16

Ok, more investigation reveals that the "Normal.dotm: File format is not valid" message happens when I try to open Excel on any of 3 different computers. Therefore the offending version of file 'Normal.dotm' must be somewhere common to all 3. The main possibility was Dropbox so I searched there and, surprise surprise, there is a version of the file. (I assume this is not where it is supposed to live?) So I deleted the file (hang the consequences, lets live dangerously!) then opened Excel on each of the 3 computers. No message. All good so far. But each time I've done this over the last month, it has reappeared a few days later, I think when I create a new file with Word...I'll test that over the next few days and report back. The bigger mystery still remains why Excel goes looking for or is sent to a Word 'template' instead of the excel version of template. Have I pointed it in the wrong direction at some stage perhaps? I'll keep looking and report back. Thanks

As has already been said, Normal.dotm is not an Excel file - it's a Word file.

Having a copy of Normal.dotm on Dropbox is of no consequence in and of itself. What might matter is whether Excel has been configured to use as its XLSTART folder the same folder that Word has been configured to store its Normal template in.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

When you go into Word, and go into File/Options/Save, is there a path to the Dropbox folder somewhere it maybe shouldn't be? Even then, I can't account for it writing the Normal.dotm file there.

On the Dropbox side, you have the desktop app version of Dropbox? Does it have entire folders set to automatically back up there? If so, you might have it pointed at the Program Files\ area which isn't a great idea.

Just a followup: The problem of "Normal.dotm: File format is not valid" seems to have gone away since I deleted the Normal.dotm file in Dropbox. So, fingers cross I've solved it. Thanks for your help and suggestions. enjoy...