How do I bridge a platform version difference between sandbox and production?

You're smack in the middle of a release cycle for the Winter '14 release of Salesforce, which brings version 29.0 of the API. Sandboxes are typically upgraded at least a month in advance of the production release, which is why your code in the sandbox is on version 29.0. You can choose your API version however on your metadata components. You have two options:

1) roll back your code to version 28.0 of the API to deploy now.

2) Wait for your instance to be upgraded to Winter '14, either this weekend or next weekend. The release schedule can be determined for your server at http://trust.salesforce.com/

Solution copied from another answer since this question ranks highest in Google for the error and we're in the midst of the Winter release.

I've just amended the trigger. Go to Setup> Develop> Apex Triggers>(SelectTrigger) Edit> Click Version Settings> Change Version to 32.0> Save. Deployed Successfully

Source: Changeset Error