SD configuration allows you to setup document splitting rules.
This sets a maximum number of SD line items on a billing document.
When SD billing is executed, it creates more than one billing document (and therefore FI document) whenever the threshold is breached by maximum 999, the system gives the error message "Maximum number of FI reached, No Accounting Document Generated"
Simply work out how many FI line items you generate per SD line item.
e.g If you create 3 FI line items per SD line item, then the maximum number of SD line item would be 333 in a billing document.
Therefore, you need to define maximum number of Line item in Billing Document.
To customize it you need to go to:
Go to IMG path -- SD --> Billing -> Billing Docs -> Country specific features.
There select your sales organization and maintain the maximum number of line items you want in billing.
Also in copy control VTFL, for your item category, you can see a field "data VBRK/VBRP" where you maintain routine 006.