"i have 8.83gb of free space out of 74.52 "
If you started with maybe an 80GB hard drive and you have 8.83GB left, that's only 11%. The Internet Download Manager is a program to accelerate downloads, that's all. Downloading 65 of anything is pushing it! I repeat, what type of files are these? If they're image or music, they will gobble up that 'space'.
Depending on your type of connection and the parameters of the site from which you are downloading, "downloading 65 of anything is pushing it."