Sometimes you may get following errors:

Unable to parse YAML file: [mapping values are not allowed in this context] at line 1
Unable to parse YAML file: [could not find expected ':'] at line 2

Both of those errors usually caused by version control system (eventually by user).
In first case svn added <<<<<<< .mine in to .meta file after conflict.
In second case it was git, added text to highlight conflict.

To fix those errors you just need to go though all .meta files and fix svn or git conflicts.

For git you can use ruby script that you can find on Ashley Whetter's Blog
For svn just adapt ruby script to look for "<<<<" inside files instead of ":" or write your own script :)