Hi,
I had the same problem with InStyle.
Check if the plugin is properly configured (plugins > Recaptcha)
If so, access your website by ftp and disable your com_virtuemart folder in the template html folder (/templates/TEMPLATE_NAME/html/com_virtuemart) - eg. add an extra letter to its name like 0com_virtuemart
Test again. If it appears, the problem is related with that override configuration.
Hope that helps.