I am trying to paypal express checkout i used https://www.sandbox.paypal.com/wsdl/PayPalSvc.wsdl. when i call use
PayPalAPIAASoapBinding paypal = new PayPalA
Just hit this myself when updating to version 119. In your generated Web service file, do a find for [][] and replace all occurrences with []. The bad guy seems to be the merchantDataField in the PaymentDetailsType.
It seems to be a bug in the Microsoft WSDL tools when interacting with services that have "nested nodes with the maxOccurs attribute set to unbounded"; I've encountered it before when interacting with FedEx SOAP APIs as well.