Hello I have an issue for invoicing tasks in project management module. Here is how i proceed : I created a product with the following features :

Product name : Website debuging

Product Type : service

Procurement Method : Make to Order

Supply Method : Manufacture

Income Account 004I 004-DEBUG EARNING 004-

Expense Account 004S 004-DEBUG SPENDINGS

I have created and confirmed a sale order for this product,it appears in the tasks. I edited the related tasks and filled it with work summary with number of hours sorresponding the the time to be spent for the task itself. Just to make it finished. I got progress 99,99% for the task

When i go to Project > invoicing > invoice tasks I find the task to be invoiced but when i try to generate the invoice i have the following error (see attached picture as well).

Integrity Error

The operation cannot be completed, probably due to the following: - deletion: you may be trying to delete a record while other records still reference it - creation/update: a mandatory field is not correctly set

[object with reference: journal_id - journal.id]

Thanks in advance for any help Yaz