I've upgrade my Alfresco installation with 20GB repository content from 4.2.C to the newest 5.0.D. Now we are having errors related to "Mandatory property not set" and "node.integrity.IntegrityException" when creating new sites, viewing tasks, etc. This errors are show in Alfresco Share page and in catalina.out logs. Please check the attached files.
Try to execute a full reindex, removing also the alfrescoModels included in Solr, it should solve your problem. This because Apache Solr actually includes an old version of the Alfresco content models and you have to remove them for letting Solr to get the newer versions.