5002 Tax group account is missing

I'm using the DI Server to add invoices, and I suddenly get "-5002 Tax group account is missing" whenever I try to make an invoice. What's strange, is that this occures only on one of my SAP-databases, whereas the others are ok. Luckily it's in a testbase. I'm pretty sure this database worked before, so I suspect someone has done something in the base. Does anyone know what generates this error, so that I can fix it?

Here is my code:

<?xml version="1.0" encoding="UTF-16"?>

http://schemas.xmlsoap.org/soap/envelope/">

<env:Header>

<SessionID>8956830C-D03A-24EA-94A6-838A5E4EEA02</SessionID>

</env:Header>

<env:Body>

http://www.sap.com/SBO/DIS">

<BOM>

<BO>

<AdmInfo>

<Object>oInvoices</Object>

</AdmInfo>

<Documents>

<row>

<CardCode>K99999</CardCode>

<NumAtCard>11311A 14:00</NumAtCard>

<Comments>11311A 14:00</Comments>

<SalesPersonCode>126</SalesPersonCode>

<U_DepartmentId>15</U_DepartmentId>

<U_Nettbank>0</U_Nettbank>

</row>

</Documents>

<Document_Lines>

<row>

<ItemCode>100312</ItemCode>

<Quantity>1.0</Quantity>

<UnitPrice>0.8</UnitPrice>

<TaxCode>U1</TaxCode>

<CostingCode>15</CostingCode>

</row>

</Document_Lines>

</BO>

</BOM>

</dis:AddObject>

</env:Body>

</env:Envelope>

And the reply:

env:Receiver -5002 http://www.w3.org/2003/05/soap-envelope"> env:Receiver -5002 xml:lang="en">Tax group account is missing 1 AddObject 8956830C-D03A-24EA-94A6-838A5E4EEA02