An error on the right hand side panel

Hello everyone. When I go to any of my pages, I see the following exception there: Error number 4001 in 4: Error while parsing velocity page Doc.WebHome Wrapped Exception: Invocation of method 'getDocument' in class com.xpn.xwiki.api.XWiki threw exception class com.xpn.xwiki.XWikiException : Error number 3202 in 3: Exception while reading document XWiki.kkembhavi Wrapped Exception: Error number 3212 in 3: Exception while loading object XWiki.kkembhavi Wrapped Exception: identifier of an instance of com.xpn.xwiki.objects.BaseObject altered from -547570503 to -278557223 Could someone please tell me what it is telling me and how I can fix that? Many thanks Ali.