GWM Excel 2013 Add-in - 'send as attachment' not working

Hello,

I created an excel add-in with the GWM Visual Studio Add-In.

The excel addin works great, except the standard MS Excel functionality: send as attachment.

If a user clicks the button 'send as attachment' (in MS Excel) nothing happens. No error, no warning.

We use the following versions:

Visual Studio 2013 Professional

Office 2013 Professional Plus

After deactivating the add-in, sending the excel file as an attachment works again.

Does anybody know the reason for this behaviour?

Thanks and BR

Tim Lutz