Yes, because this sp sp_send_dbmail is call from msdb database when you fire it from database mail.

I guess one is likely to encounter this error if upgrading from SQL Mail to Database Mail. I guess that's what you stumbled into here. Please note that you will also need that Service Broker is enabled.

However, the bigger problem I feel is that you are moving ahead without a checklist and a plan! Checking the environment before execution is one of the basic steps when dealing with configuration change. Otherwise, you might end up loosing track of what changed and what did not.

Agreed with Nakul, In past we faced same problem because of service broker was disabled after moving msdb database to other disk. Please check this post by Jacob.

http://beyondrelational.com/justlearned/posts/36/if-you-are-using-databsae-mail-and-happened-to-move-msdb-database-make-sure-to-enable-service-broker.aspx