When I set an opportunity to “Closed Won” (I haven’t tried others 
I get the following response:
Database failure. Please refer to sugarcrm.log for details.
The log file says this:
Wed Apr 16 00:11:11 2014 [25464][1][FATAL] Error updating table: opportunities: Query Failed: UPDATE opportunities
SET name=‘My Opportunity Name’,date_modified=‘2014-04-15 23:11:09’,modified_user_id=‘1’,created_by=‘1’,description=NULL,assigned_user_id=‘1’,opportunity_type=‘Existing Business’,campaign_id=’’,lead_source=‘Existing Customer’,amount=520,amount_usdollar=520,currency_id=’-99’,date_closed=‘2014-04-11’,next_step=NULL,sales_stage=‘Closed Won’,probability=100,=NULL
WHERE opportunities.id = ‘7a8cfcaf-f580-5549-cb5f-53467786041f’ AND deleted=0: MySQL error 1064: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘=NULL
WHERE opportunities.id = ‘7a8cfcaf-f580-5549-cb5f-53467786041f’ AND’ at line 2