In Money 2005 onwards, there are two versions of the budget. One is called the 'Essential' budget, which is a very limited set of budgeted items and operatons. The other is the advanced budget - this is the budget which has been in Money since about 2001 or 2002 and provides much more detail about your spending.
Some users have complained that after using the Essential budget, they have decided to move to the Advanced budget, and the program doesn't allow them to.
One fix is to remove your budget entries and categories from the essential budget for the current month and then try changing to the advanced budget again.
It is recommended that a backup is made as you're removing data to swap the budget, and if you don't like the Advanced budget, moving back would mean the old budget is lost.
Keywords: essential, budget, advanced