A tag is empty or just containing spaces. Space are ignored, due that introduction spaces are trimmed in HTML. This tag is probably really empty or it can be due to a previous error. Tidy is trying to correct the tags of the page.
This can also be a side effect of a tag being implicitely closed by another one just following.
Remove the tag.
BAD <font size=2></font> BAD <font size=2> </font> BAD <font size=2> </font>
Here is a sample of a <p> tag implicitely closed by a block tag <table>. And then <p> is empty. See the defintion of <p> for more info
BAD <p><table>...
None