Update:

Using Firefox and Firebug (god bless it), I see that there is an error in the line 601 of the backlogs JS file, in my project is the file openproject_dir/public/assets/backlogs/backlogs-2d4e6cba4393e52d0242621d2d4c432d.js. This file in the line 601 have:

RB.Task = function(e) {
    return RB.Object.create(RB.WorkPackage, {initialize: function(t) {
            this.$ = e(t), this.el = t, this.$.addClass("task"), this.$.data("this", this), this.$.find(".editable").live("mouseup", this.handleClick), this.defaultColor = e("#rb .task").css("background-color")
        }, beforeSave: function() {
            if (!this.el || !e(this.el).hasClass("dragging")) {
                var t = this.$.find("select.assigned_to_id").children(":selected").attr("color") || this.defaultColor;
                this.$.css("background-color", t), this.$.colorcontrast()
            }
        }, editorDisplayed: function(e) {
            e.parents(".ui-dialog").css("background-color", this.$.css("background-color")), e.parents(".ui-dialog").colorcontrast()
        }, getType: function() {
            return"Task"
        }, markIfClosed: function() {
            this.$.parent("td").first().hasClass("closed") ? this.$.addClass("closed") : this.$.removeClass("closed")
        }, saveDirectives: function() {
            var e, t, i, n;
/* HERE */  return e = this.$.prev(), t = this.$.parent("td").first().attr("id").split("_"), i = this.$.find(".editor").serialize() + "&parent_id=" + t[0] + "&status_id=" + t[1] + "&prev=" + (1 === e.length ? e.data("this").getID() : "") + (this.isNew() ? "" : "&id=" + this.$.children(".id").text()), this.isNew() ? n = RB.urlFor("create_task", {sprint_id: RB.constants.sprint_id}) : (n = RB.urlFor("update_task", {id: this.getID(), sprint_id: RB.constants.sprint_id}), i += "&_method=put"), {url: n, data: i}
        }, beforeSaveDragResult: function() {
            this.$.parent("td").first().hasClass("closed") && (this.$.children(".remaining_hours.editor").val(""), this.$.children(".remaining_hours.editable").text(""))
        }, refreshed: function() {
            var e = this.$.children(".remaining_hours.editable");
            e.toggleClass("empty", e.is(":empty"))
        }})
}(jQuery)

Look the line where I write HERE, in that line is the error, when he trying to do this.$.parent(“td”).first().attr(“id”).split(“_”), occurs the error TypeError: this.$.parent(…).first(…).attr(…) is undefined

Debugging I see that this.$.parent(“td”) gets nothing, and obviously this.$.parent(“td”).first().attr(“id”) is undefined. And this.$.prev() is empty too.

Thats the error, I’ll keep seeing what is happening and try to resolve it.

See the screenshot below.

Anybody ?

I did not look into the Javascript on my browser, but I had the exact same symptom. It was because of my Workflows not being set up properly. Check your global settings Workflows. You should have a Work Package Type called “Tasks” or whatever you have named it. Make sure the various roles (I use Product owner and developer) have workflow access for that Type, check every box off for now. Make sure your role can change the status of the Task Work package to all statuses. Then make sure you Backlogs configuration has the Task Type set to whatever WorkProduct Type you use for Tasks.

Maybe this isn’t the problem you are seeing, but I had very similar symptoms before fixing my workflow like this.