I resolved my problem! The Expense account was missing. As Sales and Purchase items, the fixed assets also get the G/L accounts from the Warehouse or Item Group depending on your settings, I believe those accounts are not used because the Fixed Assets module has its own G/L account determination but that's the way it works.
My case I set G/L Accounts by Item Level. This way the accounts are gotten from the warehouse as default values but can be edited in the Item Master Data. I left blank the Expense account in the warehouses because it is different on each item. To resolve the problem, I had to set a default Expense account in my default warehouse.
Hope it helps,
Regards