You need to give us a little more information, but this is what you can try.
See in your php.ini to ensure that file uploads are allowed.
Then, make sure you have the correct permissions on the uploads directory so that the web server can write to it.
A fail-safe but less seure option is to run chmod 0777 dirname on Unix and Mac OS X server. On windoze, you can right-click on the folder and then choose Sharing. This will bring up the Sharing panel. Choose share this folder.
Depending on your OS, you may be able to upload files without this step.
Hope this help, if it doesn't just give us some lines of code! 😉
