Since duplicate place holders result in an error. And you have none.
Also it is not saving the placeholder.
I can only suspect two items.
1. File/folder permissions are incorrect.
2. cache_builders folder is corrupted. This where the script creates the default islands in the cache folder.
3. if this is a post island the same applies but it is created in the cache_builders/custom folder.
If you have the mysql logs enabled in UBB that might also give you a clue.
