I have my sims living in the Reef Finery lot from the Island Living EP. I kept the house more or less the same architecturally, but I was having issues with the tiny room in the centre of the lot. I had been using it as a downstairs bathroom, but my sims were having trouble using the sink, shower, and toilet I put in there, so I moved it a little and made it larger. Unfortunately, they were still having issues, so I got rid of the shower and the sink and just left the toilet and some wall decorations. This was done in an effort to troubleshoot what was happening...perhaps I had somehow blocked the squares they needed access to in order to use the toilet.
They are able to stand directly next to the toilet, but when I try to get them to use it, they waive around saying that they can't reach it. I have tried restarting the program, deleting and rebuying the toilet...nothing seems to help. I would really like my sims to be able to use this downstairs bathroom.
What's particularly odd is that when the bathroom was in its original location, they didn't initially have issues using the plumbing objects in there. It was a quirk that developed seemingly at random.