generate e-mail messages from MS-Word 2011 using Mail app. I get down to Step 6 in the MS-Word 2011 mail merge manager, Complete Merge, and the generate e-mail messages option is greyed out. 

In MS-Word the File>Share> E-mail attachments is active and will connect to and email using Mail app. 

I am using Excel as the data source for the Word template which is a donation tax receipt I need to issue for a charity with 100 donors. 

Thanks for any help you can offer and this is urgent. 

Erin
Unfortunately, MS Word 2011 requires you to use MS Outlook 2011 as your default mail application for the mail merge email feature to work.

You will either have to use Outlook as your default email app (even if it's only temporary) or use another solution.

I have heard good things about SerialMailer although I haven't used it personally. It's not free but you may be able to download a trial. There are versions that work with Mac OS X Snow Leopard and above.

Otherwise, you could search for Mail Merge in the Mac App Store (assuming you have it installed - you didn't specify your OS) for other options.