Post Intercompany Sales Order Invoice.

Hello,

I guess due to some modifications before, intercompany sales order invoice posting can't be performed.. the following error message is appearing : 

As I found out the problem is that "Sales Tax" and "Invoice amount" fields of Totals form are not passed to fill the PO's Vendor invoice header fields, that are custom fields.

Because of the error above I couldn't track all methods in debugger.

Can you guide me in which methods I should look and add code to pass values?

What I know is that fields from total form should be taken from displayFieldServer method of SalesTotals class.

Thanks.