Hi,

Are you using a SQL SmartObject? If so, please check the database table your SmartObject is referencing, and make sure it has a primary key specified. If no primary key is specified, you will not be able to update any records.

This errors come generally if you have only "Get list method " in your smart object . so please check your smart object that are you getinng other method ? 

if no you need to see service object and design the table with primary key to get the other method.