If you get the error message on your Budget Review page shown in the screenshot below, then here is what you need to do to fix it.
You get a negative budget because you have too much of your budget allocated to your Ad campaigns.
NOTE: The $29 you see for the Email Campaign Expense will appear regardless if you have an email campaign. This is to represent an email subscription fee that your company may have.
You need to edit your ad campaign budget allocation by the amount of money you are over budget.
In the case of the screenshot above, they are over budget by $529.
So, they would need to lower or reduce the budget of at least one of their campaigns by $529. To do this, click on the link in the red warning that says "Jump to Ad Campaigns". From here, simply click the edit button for a campaign under the Campaigns tab and lower it by $529.