You need to have 100MB free space on your hard disk. It seems that the error refers to RAM memory. In order to run the program properly, Yahoo Messenger requires minimum 512MB RAM for Windows XP and minimum 1GB RAM for Windows Vista or Windows 7. I suggest you check the other requirements on the official web page. If your computer meets the minimum requirements, uninstall and reinstall Yahoo Messenger, press Alt + Ctrl + Delete key combination, open Task Manager and close all unnecessary applications. This should fix it.