I'm not affiliated with Xanga, but in order to keep blogging, it looks like you have to:
1) Download your blog archive (a .zip of .xml files) from the Dashboard. There should be a yellow bar with a blog archive link at the top of the page. This may not be done for your blog yet, but they appear to actively be working on this for everyone (whom logged in in the last 5 years) for free.
2) Pay for a subscription to Xanga 2.0, have financially supported Xanga 2.0 relaunch, or have paid for Xanga Premium.
3) Find the Tools link on the Dashboard page and import your blog archive

"Migration" is a bit of a vague term. For people that are willing to pay for a subscription, migration means your blog is moved to the new system and re-deployed as a blog that you can see, edit, and continue posting on. For those not having paid, it merely means you will be able to download a raw-data archive of your posts and hopefully import them at some other provider. If you, like me, have never given Xanga a dime, and aren't going to now, then at least you have access to your blog posts saved in the blog archive.

Here's more info:
- http://thexangateam.xanga.com/2013/09/05/were-working-to-make-2-million-blog-archive-backups-available-for-free-download-asap/
- http://thexangateam.xanga.com/2013/05/30/relaunching-xanga-a-fundraiser/

Your blog will not be available to be hosted on Xanga unless you pay a subscription fee. If you wish to remain with Xanga, and have not purchased a subscription you can do so here: https://xanga.crowdhoster.com/relaunch-xanga

If you do not wish to pay the yearly subscription and wish to move to another blog hosting service -- the process is fairly simple. Your blog archive is in a WXR format. Wordpress.com makes the transition simple in that regard. If you have made an account on Wordpress.com follow these instructions. http://en.support.wordpress.com/import/
Other hosting services may have different requirements, and you may need to look for conversion tools or copy/paste the entries manually.

@yipning If you are a free member of Xanga, unfortunately, you cannot blog on Xanga anymore, unless you pay a subscription fee. https://xanga.crowdhoster.com/relaunch-xanga

If you wish to pay for a subscription, your account will be upgraded so that you can upload your archive.

That being said, if you do not wish to remain on Xanga, there are a variety of other bloghost providers, that offer service for free. Since you have downloaded your archive, you are free to choose to go wherever you want. The easiest of these, would be Wordpress.com since your archive is already in the proper format. You'll want to extract your files out of the ZIP folder, and this will give you XML files of your blog. If you set up a new blog on Wordpress.com -- simply follow the import instructions for each XML file: http://en.support.wordpress.com/import/ Make sure to select Wordpress as your import option. Other bloghosts may have their own unique importing methods, and may require conversion tools or other steps to move.

I'm very sorry that you have some errors in your files, unfortunately I'm not an employee of Xanga, and do not know what options you have to correct that. This is the best advice I can offer.