flamingbear: I had the same problem. I see it popping up all over this board.
I fixed it by hacking wp-admin/admin.php in the following way:
@@ -83,7 +83,7 @@
if (! file_exists(ABSPATH . "wp-admin/import/$importer.php"))
die(__('Cannot load importer.'));
- include(ABSPATH . "wp-admin/import/$importer.php");
+ require_once(ABSPATH . "wp-admin/import/$importer.php");
$parent_file = 'import.php';
$title = __('Import');
Basically this just means change ‘include’ to ‘require_once’ on line 86 — somehow the file’s getting included multiple times and causing the class redeclaration error.
This doesn’t address the real problem, which is why some people aren’t having this problem while others are, why some people are getting it included multiple times… so this might break at some other time down the road. But since you aren’t importing all the time it should fix things long enough to get it done.