Move your EQ directory out of Program Files, then download, extract, and overwrite
P99Files44.zip into your EQ directory.
Also, this post is super confusing. If a file is literally disappearing from your hard drive then you have bigger problems than just P99 not working, and you might want to consider a complete format, disk defrag, and OS reinstall. Files don't just disappear unless you have either a serious hard drive issue or a serious malware issue.