UserFieldsMD update error

Hi everybody

If I try to update a UDF I get the following error:

"[CUFD] , '[Microsoft][ODBC SQL Server Driver][SQL Server]Fehler beim Konvertieren von Datentyp nvarchar in numeric.'"

which means that an error ocured while converting nvarchar to numeric.

I use the following code:

SAPbobsCOM::IUserFieldsMDPtr uf = m_cmp->GetBusinessObject(SAPbobsCOM::oUserFields);

uf->GetByKey("OITM", 0);

uf->Update();

The GetByKey-Function works, I can access the desrciption, name, ....

I use SAP Business One 2004A (6.70.185) SP: 00 PL: 05

and DI-API 6.7

thanks for help