The following misterious error happens
Error: Your request cannot be processed at this time. The site administrator has been alerted.
I have checked this link http://carvingintheclouds.blogspot.com/2014/09/your-request-cannot-be-processed-at.html
The community is not published. In case you're working with a community that is offline or in Preview status, you need to publish the community before self-registration will work.
In my case, community is published.
The Account Owner does not have a User Role assigned. If you're creating a new Account record on the fly, especially in B2C situations, you need to make sure you assign a default account owner that also has a User Role value. Any role will do, and you can use either a workflow rule or Apex to perform the assignment.
In my case, the Account Owner does have a User Role assigned.
The site guest user does not have Create and Read permissions on the Account and Contact objects. Edit Public Access Settings for the community's Force.com site to grant these permissions, along with field permissions for any fields that are included on the self-registration form. Note that by default the site's profile will not have these permissions.
In my case, the site guest user does have Create and Read permissions on the Account and Contact objects.
Self-registration is not enabled for the community. Go to Manage Communities, click Edit and make sure the Login settings show that self-registration is enabled.
In my case, self-registration is enabled for the community.