I don't know what the exact cause of your error message is, but I see a number of issues with the code here, which could be related.
In the server function, you have the following reactive expressions:
inFile <- reactive({input$file})
inFileName <- reactive({input$file$name})
but then inside the renderTable(), you mask them, with regular values:
inFile <- input$file
inFileName <- input$file$name
So inside of the renderTable(), inFileName has some value, but in the renderPrint(), inFileName refers to a different object (the reactive expression).
if(is.null("inFile")) {
...
}
But "inFile" is never NULL. You probably want to test is.null(inFile) instead of is.null("inFile").
Later you do check for (is.null(inFile)), so perhaps you just want to keep one of the checks.
This assignment only modifies the local copies of inFile and inFileName, the ones inside of renderTable -- it won't affect the copies that are reactive expressions defined at the top of the server function.
inFileName <- inFile$datapath <- newNames
For debugging your problem, I suggest putting a browser() at the top of the renderTable() and renderPrint() code and then stepping through your code. See http://adv-r.had.co.nz/Exceptions-Debugging.html#debugging-tools for more information on how to use the debugger.