I have used the composer without (major) problems before, and I tried using it now after quite a while, and it just wouldn't work. I got all kinds of shockwave errors, and with new adobe shockwave versions, more installation issues.
I finally managed to get it to work, and if anyone else is facing similar problems, I hope this will help.
Go to the "Shockwave player" section and download the shockwave player uninstaller, and uninstall the shockwave you currently have (if any).
Then download and install the shockwave "Full Installer" (the slim installer won't do).
Restart your browser, and you should be composing music in no time!
The composer on Wholenote has its problems, but for a free service it is quite remarkable. Hope this helps other users.
Sorry if this is a repost.