issue in data processing and column names in rshiny using reactive function

Question

I have changed the code a bit now but still some error I am getting, I am getting some or the other error during data processing. I am uploading one CSV file and want to do some data processing and during the process i am getting errors. Follwing is the current sample code

ui <- dashboardPage(
  dashboardHeader(title = "Inventory Management" , titleWidth = 800)
  ,dashboardSidebar(sidebarMenu(menuItem("data", tabName = "Page1" , icon=icon("tachometer"))
      ,menuItem("Analysis", tabName = "Page2" , icon=icon("tachometer"))))
  ,dashboardBody(
    tabItems(
      tabItem("Page1",fluidRow(column(3,fileInput("file1", "Previous Month close Sales office")))
       ,fluidRow(column(3,box(dataTableOutput("tabel1")))))
       ,tabItem("Page2", p("Analysis Outcome"),fluidRow(column(3,box(dataTableOutput("state_lst1")))))
            ))
               )

server <- function(input, output){
  data_uploaded1 <- reactive({
    file1 <- input$file1
    if(is.null(file1)){return()} 
    read.table(file=file1$datapath, sep=",", header = T, stringsAsFactors = T)
  })
   output$tabel1 <- renderDT(data_uploaded1())
  output$state_lst1 <- reactive ({
    tabel2 <- renderDT(data_uploaded1())
    Prv_mnth_so2 <- tabel2()
    #if(nrow(Prv_mnth_so2) >0){
      #if(is.null(Prv_mnth_so2)){return()}
    colnames(Prv_mnth_so2) <- c("GST_ward","Category","order_and_section","combo","Product_Number","Orders_Status","Option_Number","SRN",
                                "Quantity_On_Hand","Invoice_Or_Billing_Id","Lc_Amount","Clearance_date")
    #}
    Prv_mnth_so2$state <- data.frame(sub("\\-.*", "", Prv_mnth_so2$"GST_ward"))
    state_lst <- data.frame(unique(Prv_mnth_so2$state))
    state_lst
    }
  )
  }
shinyApp(ui, server)

I am getting following Error now

Warning: Error in tempVarsPromiseDomain: argument "name" is missing, with no default
  [No stack trace available]*

I am uploading file in following format Headers

'GST ward'  'Category' 'Order & Section' 'Combo' 'Product_Number' 'Orders Status' 'Option_Number' 'Shipment Reference number' 'Quantity_On_Hand' 'Invoice_Or_Billing_Id'  'Lc_Amount' 'Received month

values

Assam-18 ESC J9K619328319 J9K6193283193C743PC 3C743PC Not invoiced ACJ 7SCA47333373 150 CR4786386A 108 JAN20