border-radius attribute does not validate

Here is the contents of my selector:

..grid_16 {
     clear: left;
     -webkit-transform: rotate(-.5deg);
     -moz-transform: rotate(-.5deg);
     -ms-transform: rotate(-.5deg);
     -o-transform: rotate(-.5deg);
     transform: rotate(-.5deg);
     margin-top: .5em;
     margin-bottom: 1px;
     -moz-border-radius: 20px;
     -webkit-border-radius: 20px;
     border-radius: 0.8333em;
     box-shadow: 2px 3px 5px #000;
     background-color: #FFF;
}

I recognize that many of these are hacks built into particular browsers, 
but those are not my question.  Relative to the rest of the document, 
the line 'border-radius: 0.8333em;' is on line 28.  However, the 
validator gives me this result when I validate for CSS Level 3:

28 	.grid_16 	Parse Error[empty string]


This must be in error.  I have tried it with a different value as well 
(10px - my line-height is the default 12px, so 0.8333em is 10px).  The 
same problem occurs.