validating vertical-align

[impulse]

I received the following error when validating my code. Why?

Line 245, Column 90: there is no attribute "vertical-align".

…4d4d4" align="center" vertical-align="top">

<table width="177" border="0" bgcolor="#d4d4d4" vertical-align="top" align="center">

[Fang]

"vertical-align" in not a valid attribute (http://www.w3.org/TR/html4/index/attributes.html), it's a css property (http://www.w3.org/TR/CSS21/propidx.html)
<table width="177" border="0" bgcolor="#d4d4d4" style="vertical-align:top;" align="center">

[impulse]

Thanks!