If you're playing it during the night (on your DS clock), it could be the bug after pre-confession. The solutions are here.I used max action & max stats cheat codes, then clear Nene's route (became her boyfriend)
When i was on real time mode, sometimes it recommend me to call her for the date. But i couldn't select anything on phone screen (include "invite to a date" option). And when i clicked "back" to choice other options, it was always tell me should call her and repeat like that. It was make me restart the ds, then and got her angry@@
sr my bad english
https://sites.google.com/site/loveplustrans/troubleshooting#TOC-Game-Bugs
In your case, try to wait until it's daytime and try this part again.