Cannot save file

Hi there, I haven’t been able to make changes to my model for two days as I cannot seem to save it. I keep getting the below error. May I know if there is a solution to this? Thank you
image

I just tried to create a new model and save and it worked well. Does anyone know what could be wrong with my previous model such that I cannot save?

Thank you

If you’re willing to attach a copy of the model here in the forum, I’d be happy to take a look at it.