Hi
Thanks for sharing the code.
Could you please tell me what does exactly happen while failing? Does CanPutXMP() generate any exception or just return false value?
Certain things I want to clear you regarding XMP is that your file will not be updated until you call CloseFile() method. So may be the problem could be in your usage of XMP. You need to provide OpenForUpdate flag while opening file if you want to update a file. You may get problem during serializing to Buffer. If you are editing metadata in a loop by opening and getting metadata from a file then make sure to call CloseFile() in loop.
It is not possible for me to get exact point where it is getting fail. Could you debug your code by getting inside CanPutXMP() method and point me where exactly the problem is arising? You can also check the value for metaBuffer just before where CanPutXMP() is getting failed.