I had this issue with a facebook application that I was developing for a fan page tab. If anyone faces this issue with a facebook application then
1-goto https://developers.facebook.com
2-select the application that you are developing
3-make sure that all the link to your application has tailing slash /
my issue was in the https://developers.facebook.com->Apps->MYAPPNAME->settings->Page Tab->Secure Page Tab URL, Page Tab Edit URL, Page Tab URL hope this will help