~ap6.tmp is a file from Microsoft corporation that is used with Windows Media Player. It is part of the codex for playing MPEG-4 video files. In and of itself it is not a problem, although it has been documented before as infected by Trojan horse software.
A corrupt, infected, or missing ~ap6.tmp file is only one of many reasons that Windows Media Player might be having problems with certain video files. Searching for the problem manually can be time consuming. ZookaWare PC Cleaner can perform a free scan to identify all missing, corrupt, or infected files.