404 error code after submit

Hi

I am hosting on Websynthesis, (php 5.3.10-1ubuntu3.8, MySQL v5.5.32, WordPress 3.6, Gravity Forms Version 1.7.1) and getting a 404 error after submission
The url it is redirected to is the page with an additional ‘:/’

so submission from http://www.mydomain.com/test is redirecting to http://www.mydomain.com/test/:/ which is causing a 404

Any ideas why this might be happening?
Thanks
Anne

http://wordpress.org/plugins/gravity-forms-custom-post-types/