I got this error while performing export of SharePoint site with stsadm and sharepoint designer.
It was happening because ShaerPoint Site was searching for the following feature "PWAProposals" which was present in my dev machine and not in my production . I was able to move it successsfully before as i used stsadm-backup but it started failing with stsadm -export.
Just copy the feature from your source server ---> destination server and install the feature. This will resolve the issue . Well this is not ideal solution . I am still in process of figuring out the reference to the feature in order to remove it from list template.