The capability to receive files over Yahoo chat seems to be broken in gyachi for a couple of versions.
That feature used to work.
It seems sending files still works though.
If you are trying to receive a file in gyachi, with an instance that has been running a few hrs, or more, then yes, frequently the receive fails. This has always been a problem. quitting gyachi in this case, and restarting a new instance, will be able to successfully receive (and send) a file.
I just verified both the problem with an instance that was up for a day or more, and after restarting, I was able to successfully receive a file.