I had the interesting dilemma of TweetMeme failing on one of the sites I manage over the weekend. If you're using the TweetMeme plugin on WordPress to send your posts to Twitter you may encounter this problem. You'll see a question mark instead of the number of tweets, and when you try and tweet a post using the TweetMeme button you'll be directed to a 404 page on TweetMeme's site.
I did what anyone would do; reinstalled the plugin, updated it to the latest version. The problem still persisted so after hunting around to see if others had the problem and how they fixed it, I can offer this solution which will probably work for you.
Firstly, check your .htaccess file via FTP and make sure that any links there are relative, not fixed. If you don't know much about .htaccess or FTP, ask your webmaster or hosting service for help. If you're not using a huge range of plugins, this probably won't be the issue anyway.
The real issue is more likely the permalinks on your posts. Permalinks, for those who don't understand the term, are the addresses of your post which show up in the address bar of your web browser.
If you include punctuation marks such as apostrophes, or more than one dash in row, for example, you will force an error.
Those extra dashes and in particular that apostrophe made TweetMeme throw a wobbly. The UTF-8 code behind those characters was something it didn't recognise. If that sounds like gobbledegook to you, don't worry about it, knowing the finer points of the theory aren't important. Knowing how to fix it is.
If you're getting TweetMeme errors look at the permalinks on pages the errors are occurring, and get rid of commas, apostrophes, extra dashes, question marks, exclamation marks and other punctuation. Make sure the permalink doesn't end on a period or full stop. Your permalink may now look a little odd grammatically but the improved code behind it will make it easier to tweet about and may assist some of your other plugins to work better too.