There does not seem to be much "answered questions" on this forum -- more like a gripe forum - but I'll give it a shot:
I occassionally do file transfers between my mac and pc, using a connected ethernet cable -- and have had no problems with this until after I did a successful transfer today. Then I was not able to do another. I looked at my Local Area Connection settings - Details - and noticed that the Autoconfiguration IPv4 address that was once there, was no longer there. This may explain why the mac was not able to 'find' the pc -- but I'm not sure. Looking at other sites on the web, it appears there should not only be a Autoconfiguration IPv4 address (which was there before, because I took the IP address 169.254.xxx.xx address from there before) - but there also should be an Autoconfiguration IPv4 'enabled' [yes] setting there also, which also does not appear in my settings. I suspect I must have inadvertantly changed a setting when I did the last transfer, but do not know what or how to correct it. Thank you!