Moving emails in mail

[Peter Curtis]

Hi all

There are quite a few emails I wish to store in mailboxes for future  
use, no problems in the past however just recently when moving some  
emails I get the following message:

The message “Re: WA Ozi-Explorer user” could not be moved to the  
mailbox “Detecting/Tengraph — On My Mac”

Any obvious reason for this that I'm missing?

Regards
Peter