HT203177 iMAC & maverich Time Machine error message "unable to complete backup folder

Question

iMAC with OSX10.9.4 ; 8GB ram ; two partitions external disk formatted MAC jurnaled ; connected via Fire Wire or USB2 .
During Backup the sistem get stack and display into the "details window"  Time machine was unable to complete the backup because unable to complete the backup folder.
This problem happens with USB and Fire Wire.
The file backups.backupdb is excluded from virus scanning.
Also happens time to time that (without doing things) both the partitions of the external disk disappaire from the desk-top and a message "the disk must be ejected properly" is diplayed.
This two problems are independent une to the other.
I have change the backup disk but both the problems persist.
Thanks for any help
Gian Luigi

Answer 1

These instructions must be carried out as an administrator. If you have only one user account, you are the administrator.
Launch the Console application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Console in the icon grid.
The title of the Console window should be All Messages. If it isn't, select
          SYSTEM LOG QUERIES ▹ All Messages
from the log list on the left. If you don't see that list, select
          View ▹ Show Log List
from the menu bar at the top of the screen.
In the top right corner of the Console window, there's a search box labeled Filter. Initially the words "String Matching" are shown in that box. Enter the word "Starting" (without the quotes.) You should now see log messages with the words "Starting * backup," where * represents any of the words "automatic," "manual," or "standard."
Each message in the log begins with the date and time when it was entered. Note the timestamp of the last "Starting" message that corresponds to the beginning of an an abnormal backup. Now
CLEAR THE WORD "Starting" FROM THE TEXT FIELD
so that all messages are showing, and scroll back in the log to the time you noted. Select the messages timestamped from then until the end of the backup, or the end of the log if that's not clear. Copy them to the Clipboard by pressing the key combination command-C. Paste into a reply to this message by pressing command-V.
☞ If all you see are messages that contain the word "Starting," you didn't clear the text field.
☞ The log contains a vast amount of information, almost all of which is irrelevant to solving any particular problem. When posting a log extract, be selective. Don't post more than is requested.
Please don't indiscriminately dump thousands of lines from the log into this discussion.
Please don't post screenshots of log messages—post the text.
☞ Some private information, such as your name, may appear in the log. Anonymize before posting.