A coworker of mine ran into this error recently, while migrating a document library from SharePoint 2003 to 2007:

“A WebPartZone can only exist on a page which contains a SPWebPartManager. The SPWebPartManager must be placed before any WebPartZones on the page.”

He saw this when he tried to see the All Documents view for the library.

After looking into it, we figured out what had happened.  He was migrating documents using the Explorer View in SharePoint.  He had copied the contents of the library from one server (a remote server that we didn’t have administrative access to) to his desktop.  He then opened an Explorer View of the new library and copied the files to it.  Well, it turns out he had copied the hidden “Forms” folder, which contained the files necessary to display the different views for the library. (He had set his explorer to show hidden files, which made them visible.)

So, he had copied the 2003 forms to the 2007 library, which are incompatible.

We fixed it, by simply deleting the new document library, recreating it, and then copied everything except that hidden Forms folder.  Another option might have been to create a new document library on 2007, and copy the Forms folder from it to the broken library.  Since we didn’t need to save anything in the broken

BTW, I confirmed my suspicion with this blog post: http://palmettotq.com/blog/?p=54