What does this mean: "The form datasource query object does not support changing its AllowCrossCompany property after the form has executed the query."?

I have made a form with datasources vendtable and vendtrans.

Inside vendtable_ds.executequery() looks like this:

QueryBuildDataSource queryBuildDatasource ,queryBDS_VendTrans_Invoice;

;

queryBuildDatasource = this.query().dataSourceTable(tablenum(vendtable));

queryBDS_VendTrans_Invoice = this.query().dataSourceTable(tablenum(vendtrans));

if (curext() == "MASTERCOMP")
{
this.query().allowCrossCompany(true);
}
else
{
this.query().allowCrossCompany(false);
}

//FilterVendorName = stringedit control on form

if (FilterVendorName.text())
{
queryBuildDatasource.addRange(fieldNum(VendTable,Name)).value(strfmt("*%1*", FilterVendorName.text()));
}
else

{
queryBuildDatasource.clearRange(fieldNum(VendTable,Name));
}

//FilterInvoiceNumber = stringedit control on form

if (FilterInvoiceNumber.valueStr() == "")
{
queryBDS_VendTrans_Invoice.enabled(false);
}
else
{
queryBDS_VendTrans_Invoice.enabled(true);
queryBDS_VendTrans_Invoice.clearRange(fieldnum(VendTrans, invoice));

}

if (FilterInvoiceNumber.text())
{
queryBDS_VendTrans_Invoice.relations(true);
queryBDS_VendTrans_Invoice.addRange(fieldnum(VendTrans, invoice)).value(strfmt("*%1", FilterInvoiceNumber.text()));

}

super();

If FilterVendorName is empty and ,FilterInvoiceNumber is empty there is NO ERROR.

If FilterVendorName is NOT empty and ,FilterInvoiceNumber is empty there is NO ERROR.

If curext() is NOT "MASTERCOMP", there is NO ERROR.

The error only occurs when FilterInvoiceNumber has a value AND (curext() == "MASTERCOMP").

However, the error only happens on the first time vendtable_ds.executequery() is run. If I run vendtable_ds.executequery() a second time or third or fourth, there is no error.

Despite the error message, correct results are returned from vendtable_ds.executequery() .

I've stepped through this code and the error happens inside the super() of vendtable_ds.executequery() .

There is NO other place in that form where AllowCrossCompany is being set. The ONLY place it is referenced is in vendtable_ds.executequery().