Skype's latest update imposes a 300MB file size restriction on the size of files that may be shared via Skype chat.
Microsoft wants users to migrate to its OneDrive service which will accommodate larger files. If you routinely use Skype's chat to share audio files (and those files are larger than 300MB), consider an alternative file sharing service such as Microsoft's OneDrive or DropBox. I learned this the hard way after a late-night recording session's audio file wouldn't transfer to my co-host/editor. We had shared audio files via this method for over a 100 episodes, but it looks like those days are over. Anywhoo... I just thought I'd pass on this discovery in the hopes that it will spare someone else a headache.