The name in a general entity reference must be one of those declared in the DTD if there is no default general entity. The name in the reference has not been declared, but is close in its spelling to a declared entity's name. That entity has been used.

#0115   Markup Error

ISO 8879, 9.4.4.1

The name in a general entity reference must be one of those declared in the DTD if there is no default general entity. The name in the reference has not been declared, but is close in its spelling to a declared entity's name. That entity has been used.