I've been playing sessions of 2-4 hours without unpausing as I am in a building phase. Once in a while I get script errors for my test sim like these I've just uploaded, though I haven't done anything with her during the play session. I'm guessing this isn't serious, but I thought it might warrant checking out. What do you think?

It's Tagger throwing those errors. Although it looks like they are on the sim, they are actually on the sim's houseboat. Not sure why, but the mod is having trouble devising or working with the houseboat's map tag. Could be a glitch with the mod, but might you have actually been working on that boat or lot at the time these fired? You're right though, they don't look very serious unless you are getting thousands of them in your face all at once.

How could there be a houseboat? I don't have Island Paradise! I have some lots that were made by someone who has IP though, could that be it?
Or: it's in Lucky Palms, where they have those pseudo-houseboats that are really piers on the lake. But she doesn't live in one of them, nor does she own any kind of vehicle.

System.NullReferenceException: A null value was found where an object instance was required.
#0: 0x00027 callvirt in Sims3.Gameplay.Sims3.Gameplay.EditTownModel:get_PlacingHouseboat () ()

I didn't catch your lack of the IP expansion. Yes, that would explain the error. The lot is called Nefertiti’s Abode and is owned by Kitty Price, if that's any help.

Oh, or at least that is the sim's homelot. I guess the one with the houseboat that cannot really exist could be elsewhere.

The lot came with the world. It was overly furnished with what I guess was intended to look like tacky attempts at modern art, and I removed most of that. Why would the game think she had a houseboat? Do I need to worry about this? Is there anything I can or should do about it?

As I said, I may have read the log incorrectly. That is her home lot, but it could have been a different unspecified lot somewhere in the world that produced the error. I would do some searches within the world (on the world lot and City Hall) with MC's Object Stats, filtered to local, global, non-inventory, etc. looking for objects that don't seem to be defined and flush them. Or if that's no help, strongly consider getting rid of any lots designed by someone using IP if IP is not going to be in play.

Here are some objects I found in the list that look suspicious to me--but I haven't flushed them because I don't know what they are:
Core.FailureObject (there are 18 I think)--thumbnail is a white cube
Core.Null (there are 5)-its thumbnail is a white cube
Core.Forwarder(there are 11)-its thumbnail is a yellowish vertical rectangular prism possibly with a slot near the bottom
Core.ForawderNoImportExport(there are 3)-its thumbnail appears to be a ninja with a spear
SharedFamilyInventory (there are 26)--it has no thumbnail

I agree that the Failure and Null objects sound suspicious. As does Core.Forwarder.
The NoImportExport ones I see and flush all the time. I think those are the ones that appear as music boxes in my game (but really aren't).

Perhaps it's best to wait for Chain or one of the others to confirm which are safer to flush out and which, if any, are best left alone.

Thank you, I'll wait. Though I did decide to remove FloraFlora's lots till I can launder them through a throwaway neighborhood. I did delete the residential ones and forgot that I had placed a couple of her community lots also, but I didn't get any script errors this time. I should add that the reason I thought the SharedFamilyInventory was suspicious is that this neighborhood is very sparsely inhabited yet, and does not have 26 resident households.