Server is unable to find or scan files

Hi,

it looks like my server runs normal, but I'm not able to play a movie and he doesn't add the new movies in library folder. I don't know when this startet, probably 2-3 weeks ago.

The Server got access to the folder, an finds the subfolders (according to the status in the menu bar) but he won't add or refund any movie. I tried:

• new library
• Update to the news Plex Pass Version
• Reboots

but nothing helped. The "Plex Media Scanner.log" show very much of this entries:

Jan 01, 2016 22:36:34 [0x7000002a0000] DEBUG - Streams didn't change in analysis, not saving.
Jan 01, 2016 22:36:34 [0x7000002a0000] DEBUG - Updating media item 11038, size=7296624070, metadata_item_id=4889
Jan 01, 2016 22:36:34 [0x7000002a0000] DEBUG - Updating part with ID=13078 [/Volumes/videos/Filme/Back to the Future II (1989)/Back to the Future Part II (1989) [tt0096874].mkv]
Jan 01, 2016 22:36:34 [0x70000021d000] DEBUG - HTTP requesting GET http://127.0.0.1:32400/:/metadata/notify/changeItemState?librarySectionID=1&metadataItemID=4889&metadataType=1&state=-1&mediaState=thumbnailing
Jan 01, 2016 22:36:34 [0x70000021d000] DEBUG - HTTP requesting GET http://127.0.0.1:32400/:/metadata/notify/changeItemState?librarySectionID=1&metadataItemID=4889&metadataType=1&state=-1&mediaState=idle
Jan 01, 2016 22:36:34 [0x7000002a0000] DEBUG - Analyzing media parts for item 3985 (Zwei Tage, eine Nacht)
Jan 01, 2016 22:36:34 [0x7000002a0000] DEBUG - [ID 12693] Media part analysis: /Volumes/videos/Filme/Two Days, One Night (2014)/Two Days, One Night (2014).mkv
Jan 01, 2016 22:36:34 [0x70000021d000] DEBUG - HTTP requesting GET http://127.0.0.1:32400/:/metadata/notify/changeItemState?librarySectionID=1&metadataItemID=3985&metadataType=1&state=-1&mediaState=analyzing
Jan 01, 2016 22:36:34 [0x7000002a0000] ERROR - Exception analyzing media file '/Volumes/videos/Filme/Two Days, One Night (2014)/Two Days, One Night (2014).mkv' (boost::filesystem::file_size: No such file or directory: "/Volumes/videos/Filme/Two Days, One Night (2014)/Two Days, One Night (2014).mkv")

I can assure the files are there. I access them with the finder or the terminal with the same user, Plex is running.

Can anybody tell me what's going on and how to get the system running again?
Thanks, and happy new year,
Kai