As the name suggests, It is an error of View State. The maximum view state size limit (135KB) exceeded is the error message pertaining to View State error in salesforce and here follows a brief detailing of the issue.
View state error in salesforce holds the state/size of the visual force page that includes the components, field values, and controller state. This is important in the light that salesforce provides only a standard size of 135kb for any individual page. If the size of a particular page exceeds 135kb, the page will throw a view state error.Continue reading