A client rang up last week with a problem with their SharePoint environment. On their publishing site, every time they went to view the Pages library within Manage Content & Structure they got an error. Within the ULS logs, this was found:
Unexpected System.Web.HttpException: Multiple controls with the same ID ‘xxxx’ were found. FindControl requires that controls have unique IDs.
To fix this, I went to SharePoint designer and edited the client’s site. On the Properties of the Pages library, I noticed there were two views with the same name of xxxx!
I simply renamed one of the views, and I could then see the pages under Manage Content & Structure. I’m not sure how the client did it, and why SharePoint didn’t prevent this from happening.