Clicking 'Send Mail' link gets me a 501

Hi! I just installed Simplenews and it was all fine until I went to Home > Administer > Site Configuration > Simple News > Send Mail where I get the following error message:

Method Not Implemented

GET to /~stopho/ not supported.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

Is the tilde causing the problem? I don't want the DNS server to resolve to my site until its finished, which is going to take ages, but if having the correct URL in place means it will work then, then I don't have to worry. If not, then I do! I have very little experience in any of this...