Publish to Web Error - Won't Connect to E-mail

Hello,

I have been publishing a number of Articulate Studio '13 courses to "Web" and selecting the "e-mail" option to send to a colleague. Today I was able to share two courses this way with no problem (as I have a number of times over the last two weeks with various courses), but two particular courses wouldn't send. With the troublesome courses, this is what happened: I published to "Web" successfully, clicked the "e-mail" option after the "publish successful!" box appeared, then got an error message saying:

"An error has been encountered while preparing the e-mail. Either there is no default mail client or the current mail client (Microsoft Outlook) cannot fulfill the messaging request. Please install or configure your mail client as the default mail client. Error Code (2)"

I know that my e-mail (Outlook) is set as the default because I've sent a number of other courses in this same way with no issue, before and after seeing this error message come up with the two specific courses today. What might be the problem with these courses? How can I troubleshoot?

Thank you!