I'm running fully updated 10.5.6 on an iMac and MBA. Occasionally I can't connect to the shared drives on the iMac from the MBA. I'll try connecting, but get a "connection failed" error after a minute or so. The firewalls are set up to allow screen/printer/file sharing. Screen and printer sharing work fine, it's just the file sharing. A reboot (I can't recall which end; I'll have to try that) will fix things for a while but then the problem returns.
Has anybody else here seen this?