Excel - There was a problem sending the command to the program

Bring up the Excel options

Go to advanced and then scroll down to the "General" section.  Make sure that "Ignore other applications that use Dynamic Data Exchange (DDE)" is not checked.

http://social.technet.microsoft.com/Forums/en-US/officesetupdeploylegacy/thread/e45b1447-7d72-43ac-8b90-e96d274a1517