Ever since I upgraded to Lion, Time Machine has failed

Question

The subject line says it all - ever since I upgraded my early-2011 MBP to Lion, every few weeks it announces that my TM backup is corrupt and it has to start a new one.  So, I let it build a new back up - but then, a few weeks later, the problem recurs.
Looking through this and other sites, I see lots of people complaining about this with both Lion and Snow Leopard - but no explanations about why it happens.
Is there any logfile I should be looking at to determine what's causing the problem with my backups?

Answer 1

If you have more than one user account, these instructions must be carried out as an 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.
☞ If you’re running Mac OS X 10.7 or later, open LaunchPad. Click Utilities, then Console in the page that opens.
Select "system.log" from the file list. Enter "backupd" (without the quotes) in the String Matching text field. Post the messages from the last backup, beginning with "Starting standard backup."
Post the log text, please, not a screenshot. If there are runs of repeated messages, post only one example of each. Do not post many repetitions of the same message.
Some personal information, such as the names of your files, may be included — edit that out, too, but don’t remove the context.