Heres what their help page says:
" It's either a problem on the server (us), or or on the client (you).
Sometimes we stop processing submissions for an hour or so to upgrade the software. When we do, there is a huge backlog to clear, so submissions may be delayed - give it an hour to catch up.
Try to identify/fix the problem yourself, by following this easy guide:
1. Make sure you're running the latest version of the plugin.
2. Read the news on the front page of the site for clues.
3. Check the System Stats graph, it updates at the top of every hour. If it shows a sudden dip in submission numbers then just be patient; you're not the only one experiencing problems.
4. Restart your player - this will cause the plugin to re-handshake with the server and receive new instructions.
5. Check the log file for your plugin (eg: c:\program files\winamp\plugins\audioscrobbler.log). Look for enlightening error messages
6. Try some files from a different album, perhaps there is something strange about the tags in the files that aren't working. Let us know if that is the case, so we can fix the problem for the next plugin update.
7. Check that you don't have a personal firewall that is preventing Winamp from accessing the internet. (HINT: If you're not sure if you have a firewall, then you probably don't have one)"