I was having the same issues with this plugin but I have fixed it for now. I knew it had something to do with a CSS file that was being included (for this sake we'll call it "injected") into the Dashboard. I also narrowed it down to just effecting the dashboard so I dug further into the source.
Shaon, you'll need to figure out a permanent solution for this on your end but for now my work around is as follows:
- Go to WordPress Plugins folder on your server where download-manager is located
- Open, to modify, functions.php
- Scroll to line 89
- Remove line 89 and replace it with the following:
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$output = curl_exec($ch);
$output = str_replace('<link href="//netdna.bootstrapcdn.com/bootstrap/3.1.1/css/bootstrap.min.css" rel="stylesheet">', '', $output);
Now for an explanation. The problem is a CSS conflict, obviously, from what I can tell. I'm guessing (from what I could see in their source) that the latest WP version of 3.9 is utilizing Bootstrap which I'm, again, guessing has a conflict with the bootstrap being included here. Simply "remove" the bootstrap include that comes from that Widget and you're back to good graces. This problem happens even if you have the Widget "hidden" in the Dashboard as it is still generating the code just giving a "display: none" style pretty much.