Is the database a trusted folder? In A2007 and later, code will not run if the file is not in a trusted location. To check this in A2010 go to the File tab, Options, Trust Center, then click the Trust Center Settings button and select Trusted Locations. From here you can add a new location if needed.
Can you provide any more specifics about what you mean by "not working"?. Are you getting an error message? Nothing at all? Is this the only code in your app that is having problems that you know of?
I don't have any other specific suggestions for you but a search of the topic indicates that it is possibly a problem with Windows Messaging Service or how the default e-Mail program is specified, or a few other non Access specific issues. Here are a few other links you may or may not have come accross, here, here or here.