pdf can't be found (track)

I am runninh endnote X7.7.

Most of refernces pdf can’t be found by endnote. when I want to open theis mesage is appear 

(The following file could not be opened. This may occur for a number of reasons including, but not limited to: the file is corrupt or the relative link was deleted.

File D:\Sfr\EndNote Library\My EndNote Library.Data\PDF\1066551203\A high-mobility electronic system at an electr.pdf)

Please anyone can help me?