Installation error with Flashgot, GreaseMonkey, etc.

Hi,
I recently installed Flashgot and GreaseMonkey for downloading books. I also installed an anti-virus software after. All installations were successful; however, when I tried using Flashgot option "flashgot selection", I got this error. I tried reinstalling everything: Flashgot, GreaseMonkey and even my browser but still I got the same error message.
Please advise on what to do next.
The error message is something like this:

FlashGot Error
Download manager not properly installed.
Incorrect function.
Thanks in advance for helping out.
