The FAQ says 'Some people have trouble with the FET tools when using some models of IBM ThinkPad. The signal voltages seem lower than usual on these machines, and do not drive the FET tool reliably'. I met the same problem, and get it solved by changing the operating mode of the parellel port from 'Bi-directional' to 'EPP', which can be easily done through the software 'Thinkpad Configuration'.
