Problem using C# to create UDF

Hi,

i'm writing a small application in c# to create UDF .

I'm using the example written in visual basic as a reference. The problem is that the following instructions

udfInstructions.References = references;

and 

udfInstructions.VariantValues = (CpfcUDFVariantValues) variantVals

generate an error :

"Property, indexer or event pfcls.IpfcUDFCustomCreateInstruction.References" is not supported by the language; try directly calling accessor methods ..."

Can Anyone help me? How to solve?

Thanks