timeoflastkeydown

there seems to be a problem with getchar or something else, because
my experiment runs until the user hits a key more than once. he is
asked to respond and sometimes the program seems not to respond
correctly and therefore the user might type again. Then the program
fails to execute and windows gives me the error message stating that
the variable "timeoflastkeydown" is not defined. Does anybody know
this problem and have a clue what i can do about it?

philipp