Roo is installing Spring Security 3, pursuant to ROO-226 work. The XSD is the incorrect version for Spring Security 3 apps.
Upgrade security add-on to Spring Security 3.0.0.M2
I have checked and the improvements made in ROO-226 have already addressed this. From Roo 1.0.0.RC3 (or SVN trunk since revision 334) Roo does correctly create applicationContext-security.xml files with the Spring Security 3-specific XSD version.