When anonymous users login in the SharePoint site which has BDC web parts, you will see the error message “You do not have permission to access abc in xyzInstance”. This is fixed in the Infrastructure update of WSS and MOSS. In the Application Definition File, for each method instance ( for which we need to give anonymous access), we need to add a property called AllowAnonymousExecute. Its a boolean value which needs to be set as true.
<MethodInstance Type="Finder" ReturnParameterName="Products" ReturnTypeDescriptorName="ProductDataReader" ReturnTypeDescriptorLevel="0" Name="ProductFinderInstance">
<Property Name="AllowAnonymousExecute" Type="System.Boolean">true</Property>