error importing video files

hi everybody.
i have been using after effect cs5 for few months but for last few days im having a serious problem. whenever i try to import a video in .mov or .flv formats, i get an error saying unable to load file and file may be unsupported or curropted. those videos play fine in media player and i have used exact same files before. i have installed latest quicktime, re installed after effects, updated it, did a virus scan of pc. but nothing helped. this problem is really annoying. anyone please help.
thanks.
here's a screenshot

@dave. I don't remember doing anything that might cause such problem.