Not sure what when wrong with the xml as posted, try this

<customUI
xmlns = "http://schemas.microsoft.com/office/2006/01/customui"
onLoad="rxRibbon_onLoad"
<ribbon startFromScratch="false"
<tabs
<tab
idMso = "TabHome"
Tag = "TabHome"
getVisible="Tab_getVisible"/
<tab
idMso = "TabInsert"
Tag = "TabInsert"
getVisible="Tab_getVisible"/
</tabs
</ribbon
</customUI

PT