'Generate' is ambiguous because multiple kinds of members with this name exist in interface 'IClientTokenGateway'

Question

I have created BrainTreeGateway Object with following configuration.

Dim objBtGateway As BraintreeGateway = New BraintreeGateway()
With objBtGateway
     .Environment = Braintree.Environment.SANDBOX
     .MerchantId = "mymerchantid"
     .PublicKey = "mypublickey"
     .PrivateKey = "myprivatekey"
End With

after this i tried to generate client token with following statement.

Dim clientToken As String = objBtGateway.ClientToken.Generate()

This statement says "'Generate' is ambiguous because multiple kinds of members with this name exist in interface 'IClientTokenGateway'".