Error 403 started appearing

[sandzb]

This is in my log:

[Wed Mar 15 06:27:07 2006] [error] [client 127.0.0.1] (20024)The given path misformatted or contained invalid characters: Cannot map POST /results<b></b>.php HTTP/1.1 to file, referer: http://localhost/~phpdesigner_outputlocal_tmp~5374.htm

How do I fix this? Why would it of all of a sudden become a problem? Thanks.