Plugins or other programs installed on the computer system may cause problems with the good functioning of software such as Adobe Reader. If an invalid plugin is detected by Adobe Reader, the program will not be able to start. Adobe Reader quits as there may be some other program such as Babylon translation installed on the computer system. In computer systems with the Babylon translation tool installed, Adobe Reader 8.1 quits due to an invalid plugin error. Re-installing Adobe Reader will not solve the problem. The only solution is to uninstall either the Babylon translation tool or Adobe Reader.