Outlook for Office:Mac 2011 Home & Business will not open. I get a "not enough memory error"

I began getting a rebuild Outlook data base message about a week or so ago...rebuilt the data base as requested then the system would not open and gave me a "not enough memory error". Unable to get into Outlook at all as the error message pops up every time I try to get into Outlook.  All other, Office applications work fine. How do I fix. I have a MAC Pro 4 core Tower.