I am getting following error while creating new Site from a Site template.
It would seem that for some reason the content type name isn't begin resolved, so SharePoint tries to create it with the name "$Resources:IWAssociatedField,RelatedDocumentContentType". This will then fail, since a content type name cannot contain character such as ":".
You need to identify the reason for the missing resource resolution. Was the content type provisioned by a feature no more available? Was the site template "migrated" from another server? Your first priority should be confirming if the above resource exists somewhere on the server, then checking if it contains the searched key.