[This is preliminary documentation and subject to change.]
The Object Description Language (ODL) file, oleacc.odl, contains information that differs between the VB and C/C++ implementations. Oleacc.odl contains the following definition for the property-setting version of the function.
[hidden, propput, id(DISPID_ACC_VALUE)]
HRESULT accValue(
[in, optional] VARIANT varChild,
[in] BSTR szValue);
Although the varChild parameter is listed as optional in the ODL file and the object browser, you must include it when calling the property setting version of accValue.