... attribute value "..." must be lower case for XHTML

Cause:

XHTML error. XHTML is case sensitive.  The named values in XHTML should be in lowercase.

Solution:

Set the value in lowercase

Sample:

<p> attribute value "RIGHT" must be lower case for XHTML

BAD   <p align=RIGHT>hello</p>
GOOD  <p align=right>hello</p>

References:

XHTML specification: http://www.w3.org/TR/xhtml1/