Win7に入れたら削除や上書きでやけに使用中のため〜ってエラー出てたが、これが原因かよ。

It has many other flavors:

Cannot delete file: Access is denied
There has been a sharing violation.
The source or destination file may be in use.
The file is in use by another program or user.
Make sure the disk is not full or write-protected and that the file is not currently in use.