If the Charge dropdown is empty when creating a Register a Charge event, this is because no charge has been created against the company.
You must first create the charge in the company record before it will appear in the event wizard.
To Add a Charge
Go to the relevant company.
Select the Misc tab.
Click Charges.
Click New.
Enter the charge details and save.
Once the charge has been created, return to:
Events > Register a Charge
The newly created charge will now appear in the dropdown list.