Here is the method how to solve it:
1. Exit IDM from the taskbar before entering the serial.
2. Disconnect active connections to the internet.
3. Open the C: \ WINDOWS \ system32 \ drivers \ etc and locate the file 'hosts'.
4. Then right click and open with notepad. If you can not open with notepad or maybe We Are not Able to edit it, then There is a little trick to edit it,first cut "host" file ,paste it at any place e.g on desktop,then right click and select "open with notepad" to edit it,
5. Once open please copy the below text and paste it at bottom of all text below the "127.0.0.1 local host:",remember do not replace the old text just paste below text their...
6. When finished, do not forget to save (Ctrl+S), then again cut your "host"file and paste it again ,to its previous location that is(C: \ WINDOWS \ system32 \ drivers \ etc).
Open IDM, (go to start menu, internet download manager).
7. IDM registration tab will b open just put any below key , to better fill the serial number first.
To be content with the serial number is (choose one):
8. So "fake serial number problem" will be resolve itself and IDM is ready for reuse....
I hope it will work for you,See my next post i will tell you how to integrate your IDM with any browser especially with Firefox..