LR4.1 not importing video anymore.

I'm using lightroom 4.1, and it wont import video anymore. It has previously although its been very erratic both to import and play. Its not a file issue as ive tried at least 4 differnet formats that play elsewhere. Ive also removed previous imported video files in lightroom and tried to re-import. Gives same error "there is a problem with the video file (1). Have tried re-install and stopping dynamic link as mentioned in another post, but nothing makes any difference. Has anyone experienced the same and found a solution please. thanks