"Object is invalid" after three loops

Question

This script is placing objects on pages (in reverse order, as it happens). It works correctly for three pages, then stops and gives me the following error:
Object is invalid
Line: 15
Source: img = doc.pages[pageNo].place(fileList[a]);
I have no clue why, so any help would be very appreciated.
var doc = app.activeDocument;
var totalPages = parseInt(app.activeWindow.activePage.name);
var inFolder = Folder.selectDialog("Please select folder to process");
if(inFolder != null){
var fileList = inFolder.getFiles(/\.(tif)$/i);
for(var a = 0 ;a < fileList.length; a++){
if(fileList[a] instanceof File){
var fileString = fileList[a].name.split("_",1);
var fileNo = parseInt(fileString);
var pageNo = totalPages - fileNo;
img = doc.pages[pageNo].place(fileList[a]);
imgFrame = img[0].parent;
var Bound = imgFrame.geometricBounds;
var h = Bound[2]-Bound[0];
var scalePercent = 7.75/h;
var imgMatrix = app.transformationMatrices.add();
imgMatrix = imgMatrix.scaleMatrix(scalePercent, scalePercent);
if(fileNo[0]%2 == 0){
imgFrame.transform(CoordinateSpaces.PASTEBOARD_COORDINATES,AnchorPoint.topRightAnchor,imgM atrix);
} else {
imgFrame.move(["-.125in", "-.125in"]);
imgFrame.transform(CoordinateSpaces.PASTEBOARD_COORDINATES,AnchorPoint.topLeftAnchor,imgMa trix);

Answer 1

be carefull with var totalPages = parseInt(app.activeWindow.activePage.name);
the pagename can be (for ex.) "MXIV", if you use roman numbering.
use .documentOffset to be on the safe side.