... cannot copy name attribute to id

Cause:

In XHTML, the "name" attribute has been deprecated and replaced by the "id" attribute. If you want to keep both tags for compatibility reason, name and id, the values should be the same.
This error is generated when only the name exists and that tidy try to copy the value of the name in the id attribute. But an "id" must begin with a letter ([A-Za-z]).

Solution:

BAD         <a name="123456">...</a>
BAD         <a id="123456">...</a>

DEPRECATED  <a name="my_link">...</a>

GOOD        <a id="my_link">...</a>
GOOD        <a id="my_link" name="my_link">...</a>

References:

XHTML W3c spec: name attribute: http://www.w3.org/TR/xhtml1/#h-4.10
XHTML W3c spec: name and id  http://www.w3.org/TR/xhtml1/#C_8
ID W3C spec: http://www.w3.org/TR/html4/types.html#h-6.2