I want to add my custom web part in master page using SharePoint Designer.
I tried but I am receiving the error shown below.
And this is the description of error.
ExecuteRequestInSandBox call failed. System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.SharePoint.WebPartPages.BinaryWebPartSerializer.Serialize(PersonalizationScope scope, BinaryWebPartSerializerFlag binaryWebPartSerializerFlags, BinaryWebPartSerializerWriter writer) at Microsoft.SharePoint.WebPartPages.BinaryWebPartSerializer.Serialize(SerializationMode mode, BinaryWebPartSerializerFlag binaryWebPartSerializerFlags, BinaryWebPartSerializerWriter writer) at Microsoft.SharePoint.WebPartPages.SPUserCodeWebPart.EnsurePersistedBlobsMatchPropertiesCollection() at Microsoft.SharePoint.WebPartPages.SPUserCodeWebPart.GetWebPartDataForRemoteCall(Object& viewState, Object& controlState) at Microsoft.SharePoint.UserCode.SPUserCodeWebPartRemoteExecutionHelper.ExecuteRequestInSandBox(HttpContext context, SPWeb web, SPWebPartManager manager, SPUserCodeWebPart userCodeWebPart)