TestComplete shows an error message if the value of the <field name> field in the Template Editor dialog consists of the "." symbol or contains any symbol of those that are inadmissible in the node name. These symbols are: /, \, :, *, ?, ", <, >, |.
The template name will be used to refer it from tests. Therefore, the template name must be a valid identifier for the scripting language used in your project. The naming rules used in scripting languages supported by TestComplete may slightly differ from each other. To make the method name match the naming rules of any scripting language, use only alphanumeric and underscore characters in it and start the name with a letter.