I see the following message all the time, and find it the diametric opposite of helpful:
"Highlighted snap line(s) cannot be regenerated."
Yes, I do have snap lines on my views, but there is nothing whatsoever highlighted, and I can't figure what lines it refers to. It's not preventing me from doing anything, but I find this type of thing annoying. I don't like having warning messages spewed out when I open drawings. Is there any way to find out just what these vague messages are trying to tell me? Once upon a time, the snap lines that became disconnected or otherwise ambiguous would be shown in a different color, weren't they?
This same question was asked in 2010 (see below) and received no answers, perhaps I'll be lucky this time.
Ref: "highlighted snap lines can not be regenerated"
I would suggest looking at the system colors to see if the highlight color may be too close to the original color to be easily noticed. I have made changes to the system colors on my computer to ensure there is enough contrast in the highlights, selections, etc.
I had some that I purposely made unable to regenerate and they turn red (default is dark grey), so it's not that. I wish it were. I'm thinking it's just that it can't regenerate them at all, can't even represent them on screen, but still gives the warning, or maybe it's making some zero length for whatever reason.
Try looking at the drawing tree. While in the Annotate tab, you should be able to see the snap lines in the tree. Hopefully they will be marked.
Change your selection filter to "Snap Line", then zoom out and window select everything. If no snap line is obvious, try zooming in to the bottom left corner, right near the origin. Sometimes nearly zero-length lines will end up there.